A list of frequently asked questions about web bookmarks, online bookmarking (and tangentially about cataloging and retrieving information with a computer) and answers I’ve given in the past, gathered here for your convenience.

Are favorites and bookmarks the same thing?
Let me answer with another question. Are a hot-dog and a full lunch the same thing?

Why does Firefox offer both Pocket and bookmarks?
Because they are two entirely different things.

Or, let me put it another way, whould you ask “Why would you want both a car and a pair of shoes?”? ;-)

What bookmark manager would you recommend?
None. Bookmark Managers are a stopgap solution at best.
Online bookmarking is a much more mature and versatile solution.

I’m overwhelmed by my bookmarks. What can I do?
Ditch archiving and managing bookmarks in your browser(s) and move to an online bookmarking service. One that has tags. Tags are important. They help you not being overwhelmed by bookmarks.

What is the best way to manage a large collection of bookmarks (with duplicates) across multiple browsers?
If you use an online bookmarking service chances are you would have almost no duplicates. It won’t allow you to bookmark twice the same url. In particular one online service even removes the referral cruft some social networks and sharing systems add, so the probability of having two variations of the same url in your collection are very slim.

How should I manage 6000+ bookmarks? I would like to search through them based on tags and also sync across multiple browsers.
I’d like to be blunt, if I may: if you have a lot of bookmarks, and I do mean a lot, stop trying out delicious, diigo and other services get yourself an account on Pinboard. It manages without a single hitch my data, which amounts to close to 25’000 bookmark and hundreds of tags. This way you will have a universal, tested and capable tool to archive, organize and retrieve/share your url across multiple web browsers.

I’m organizing my bookmarks in chrome, but have difficulty sorting them. How would you do it?
I would (and did) ditch storing and organizing the bulk of my bookmarks and opt to use an online bookmarking service. I’d leave (and actually did) just a few often-accessed (and difficult to type or autocomplete) urls and bookmarklets plus the latest things I’m checking out/working on.

Is Pocket good enough to replace Delicious?
Nope it isn’t.
Instead of delving in a long explanation please let me answer with another question:
Is a fork good enough to replace a spoon? No it isn’t. Sure, maybe you can try and succeeed in exchanging one for the another sometimes, in some emergency situations and with some major effort on your part, but they are tools with different features and different purposes. 
They are not interchangeable. And they are not exclusive: they are complementary. The same holds for Pocket (or Instapaper) and Delicious (or Pinboard).

If the app Pocket adds social features like Delicious, what will it look like?
For the same reason why a Calendar cannot evolve into an Address Book, or a knife is a lousy pick. They’re different tools.

Why should you use Pocket when you can bookmark pages that you want to read later?
Well, three reasons come to my mind. Some of them are legitimate uses for Pocket, one is not ;-)
1. you want to “mobilize”, i.e. strip away all cruft and navigation from a long text that you wish to read
2. you read a lot on your mobile device when you’re offline
3. you are very confused about bookmarks and what they are as opposed to articles ;-)

For personal productivity, the use of Pocket is better than simple browser’s bookmarks? Is there any difference?
tl;dr: no, and yes.

Pocket is great at storing, viewing, managing and sharing relatively small sets of text content. A bookmarking system is (or should be) able to manage a huge list of url, pointing to anything from text to images and videos.
In other words if you plan to use Pocket as an alternative to a bookmark manager, a) you’re in for an unpleasant surprise, delving very quickly into chaos or b) you probably don’t really need a bookmark manager

How many websites do you have bookmarked in your web browser?
In my web browser? Very few, I want those addresses (many of them are javascript bookmarklets) to be easily accessible. But I have bookmarked more than 26000 website urls online using my web browser.
Where? And how? Well, “that’s another story”, as they said in “Irma la Douce”… ;-)

How can I organize all my files, bookmarks and notes if they are spread on many devices and accounts?
Use an online bookmarking service. A good one, that won’t buckle under the load of many bookmarks and that won’t disappear when its money/funding runs out or when it gets acquired.

How can online bookmarking increase research productivity?
Here are three ways online bookmarking can and will increase research productivity, in saving precious time and energy:
1. Recall specific sets of resources/tools/sources by using one or more personalized tags
2. Access the aforementioned data from any computer/device/place (as long as you have an Internet connection)
3. Share the data with other researchers and encourage them to do the same so your data will grow in quantity and quality

Does social bookmarking in 20XX still work?
Yes, social bookmarking still works in 20XX, and will for quite a while. That’s if you actually need to store, file and retrieve online information and resources that are relevant to you and/or your fields, interests, expertise area, etc.
On the other hand, if by “social bookmarking” you refer to things like reddit, Hacker News Evernote or other online tools and thematically organized forums or news discussion services, I cannot vouch for them since there is a high rate churn and the public (and investor) attention is fickle and very subject to change due to the latest (perceived) fad.

What are the social bookmarking sites for 20XX?
I’d say they’re more or less the same of 20XX-1. Social bookmarking is not exactly a hot trend or growth area, so the market is basically stable. Here and there new services pop up but the main players are few and well established.

Do we still need bookmarks?
It depends on what you consider “bookmarks” and how much you actually need to retrieve a list of useful and filtered web addresses on n topics Vs just “searching things”.

What are the best do-follow social bookmarking site other than these digg, fokld, Tumblr, slash, scoopit and many more?
tl:dr: the social aspect of social bookmarking is about discovering and sharing and vice versa.
It’s very difficult to give an exact and satisfactory answer, mainly for two reasons:
1. Some of the online services you mention are not and do not offer social bookmarking
2. The goal of social bookmarking has never been amassing followers, the social part has been an integral part but mainly a byproduct of sharing what you know
In other words: in social bookmarking you file, organize and possibly annotate a useful (or at least interesting) collection of online resources. You do this mainly for you. The system – if it’s a good system – allows you to find other good stuff already filtered and archived by others. On the strength of this you may or may not bond with those other “users” and maybe even gain some attention if you’re really good, but it’s never a one-way thing.

What is the best free tool with a nice appearance that can manage bookmarks, files and notes for a big single person project and personal use?
I am tempted to answer that “the best free tool with a nice appearance that can manage bookmarks, files and notes for a big single person project and personal use” is probably the Macintosh’s Finder.
Here’s why. It draws icon previews of almost any kind content, differentiating data, offers immediate preview via Quick Look, has various types of navigation, offers categorization in the form of folders and tags/colors and personalized searches, and also has links and alias, so you can have the same items readily available in multiple copies and locations.

If you could bookmark just 5 websites, which 5 you would choose?
It doesn’t make sense to have “just 5” bookmarks. For that, your memory and the url autocomplete feature of your browser will absolutely suffice. 
Bookmarks are useful for storing more, way more urls than your memory and browser can ever manage.

What is the best way to sync the bookmarks between browsers?
The best way? Not having to sync anything and storing your bookmarks online. There will be always a situation where some browser isn’t supported by extensions/utility that sync bookmarks or you will be using a third-party computer or device and will not be able to install use the syncing feature. 
Think out of the box (if you can). Store your non-sensitive bookmarks online!

Which social bookmarking and link saving websites do you use?
The one and only Pinboard.in
It’s the most no-nonsense and future-proof service out there, and it’s the heir to the Delicious legacy, if you dig the tag-based, fast-loading, hi-performance, no-bullshit approach.

What is the best bookmarking service?
There’s a lot of bookmarking services out there. Some are old, some are new, some have cool graphical features other value privacy features, some are free and some are not. I’ve tried dozens of them (and I’m still checking out new ones) but as far as url+text bookmarking is concerned nothing beats Pinboard (http://pinboard.in). Let me write that again: nothing.

What is the best offering for an online library? I want to be able to add bookmarks to be able to share with people and them to be categorised.
I’d bet my chips on Pinboard.in. Since the original Delicious’ demise I’ve been doing just that (and much more) on what is the online bookmarking service.

Is Pinboard.in better than other web bookmarking services?
Is this a rhetorical question? 
The answer is obviously: yes, it is. Pinboard.in may lack “glitz” and be perceived as “dying” (uh?) but it still outperforms all of the other online bookmarking services with its no-nonsene approach. Oh, and it’s a solid, in the black self-sustaining service. No acquisition and abrupt shutdown after VC funds have burned out…

Why have social bookmarking sites become less popular?
Are they? Or simply the dust has finally settled a bit and real social bookmarking services are still standing while those with an uncertain mission and business model are limping towards their doom?

What bookmarks do you have saved?
There are at least four types of bookmarks, as far as I’m concerned.
1. The first type are bookmarklets to share, modify or interact with web pages. They live in the bookmark bar of the browser(s) i currently use.
2. The second type are urls of online services or tools/documents I use daily and for a long of time and are too long/complex to type or cannot be invoked by the autocomplete feature of the browser. These also live in the browser(s) bookmark bar.
3. The third type are temporary bookmarks such as very specific search results, works in progress or groups of related pages or sites. I usually rely on the reopening feature of browsers and their synchronization features but sometimes I need to clean things up. These only live for a while in the browser and then get deleted or saved into my online bookmarks.
4. Finally there’s the fourth and (definitely) biggest group of bookmarks, which are infrequently accessed but are carefully archived with pertinent tags. They represent quality and useful information I plan to use or share in the future which I won’t find again in a few seconds with an online search and cannot be easily managed and accessed through any browser bookmark feature. These go into my online bookmarks, currently stored on Pinboard.in.

What is a good set of categories for bookmarks?
My suggestion is to ditch fixed “categories” and hierarchical structures and adopt multiple flat tags. This allows for a finer and more flexible taxonomy of bookmarks, so you can label, archive and retrieve information with more speed and ease.

Is there a web tool that can auto-categorize bookmarks for you?
Why would you want to do that when you can add your own tags and have a more effective and relevant form of categorization?

How can one best ‘plow through’ thousands of bookmarked articles?
By using tags. Hopefully (if not, start now!) each bookmark will have been filed with two or more tags and you can filter and focus on the stuff that matters to you.

Is there a way to enable search results from a personal Delicious account when performing a google search?
If you need to use search on your bookmarks, that means you are not using tags, i.e. UR DOING IT WRONG ;-)

What is the best way to translate “tags” in a UGC website?
There’s no reason why you should “translate” tags. Tags are a highly personal system of information categorization and by automatically modifying the user’s choice you would be undoing the significance of the original information, and doing a big disservice to the user.
On the other hand, you could try to implement and suggest to the user a set of very common tags in many languages, such as history, computer, browser, security, recipe, home, sports, money, love, etc. which, if he likes and finds useful, he could adopt.

Can I see others’ tags on pinboard.in?
Sure you can. Just go to their “home”, i.e.
pinboard.in/u:username
and the tags should be there, on the right side. 
The only exception is probably tags for private bookmarks.

What is social bookmarking and its importance?
As far as what it is and how important it can be you can start by reading the Wikipedia entry on Social bookmarking

How does Social Bookmarking work?
You painstakingly (or pretty fast and in a loose manner) urls, descriptions and tags, and they will be available from anywhere and quite searchable. The usefulness varies and depends on how much work you put in and how much you need an organized set of personal bookmarks.
It’s pretty good. 
Personally, I’d like to stress out how social bookmarking can first of all work on an asocial level just by being an awesome system for organizing loads of bookmarks, in ways which browser’s bookmark manager cannot. Then, as added bonus, you have the social aspects, which can leverage the folksonomy aspect, the network or the republishing/resharing features present in the best online bookmarking services, such as Pinboard.in.

What is the difference between directory submission and social bookmarking?
The difference is the same as in submitting an article/feature to a magazine and writing on your own blog/website.

What is the best source for learning perfect social bookmarking?
tl;dr: there is no “perfect social bookmarking”, only bookmarking that works for you.
Long version: yes, you can learn a lot from other longtime users of social bookmark sites (I try to avoid the “power user” definition). 
See how they store, tag and retrieve bookmarks, but don’t take anything they do as the “perfect” way to do it. Borrow and use their techniques and tricks, try to improve, experiment, and see what actually helps you and whatnot.

What is a good number of bookmarks to have on Delicious? And how should someone use them?
I’m close to 27K bookmarks on Pinboard, and they are quite well tagged (I have almost 2400 tags). 
Some of my bookmarks are for later reference, some are to be shared (and discussed), many of them are work-related (I write about culture and technology), and some of them “power” a couple of websites. 
Ultimately it doesn’t matter how many bookmarks you have, only if they are relevant and useful to you. If they are then tags can and will be the way to make them valuable.

Is there a better way to manage a bookmark with an extension?
Not really. An extension means you’re still tied to a specific web browser (two or three if you’re lucky and the extension has been ported to the most popular browsers), and you’re still using tools that have very low limits in managing bookmarks as they grow. 
I strongly suggest you switch to an online bookmark solution.

Is social bookmarking effective for SEO?
Who said that social bookmarking has ever been important for SEO?

Real social bookmarking has historically been hostile to link popularity manipulation and has fought tag/link spamming.

Can I get a lot of traffic/views by using social bookmarking to promote my YouTube videos?
No, you cannot. It’s not the right tool. On the other hand it can be an effective tool to reach a specific target, e.g. one or more influencers who are active users of a social bookmarking service.

Can you turn content from your web browser’s bookmarks into a profitable website?
Yes you can, although you will need to grow the content quite a lot and use a bookmarking service. “Browser bookmarks” won’t cut it, for obvious reasons.

How do you store and manage large amounts of web-acquired content, knowledge and references like articles, images, and bookmarks?
First of all you have to understand your needs and then evaluate, choose and optimize the right tools for you. 
I don’t believe in any “one size fits all” app, service or solution: e.g. I’m actually using a combination of three (actually four if you count the tagged files in my Mac’s folders) systems of storage and reference. 
Bookmarks (with snippets of text) go to Pinboard, selected full content is stored in Evernote and files and drafts in progress are always available through Dropbox (text is managed through apps such as Nebulous writer and Notational Velocity).

Are bookmarks really useful?
From what you state in your question I’d say bookmarks are not really useful _for you_. Others may have different needs, approaches and priorities.