as a web developer, i bookmark reference and resource sites especially with contents that are easy to read and follow. also like to bookmark sites with nice and unique design for inspirations.
I bookmarked sites or projects I’m working with so I can access on it right away. By that, I don’t need to memorized the URL’s, IP Address or DNS because sometimes we can’t avoid being forgetful.
Based on the responses I’ve received so far, it appears people bookmark websites for a variety of reasons - not the least of which is functionality. Besides, the reason for my post was to foster conversation among members. And it appears I’ve succeeded in doing that.
Thanks to everyone who took the time to respond. I really appreciate it. 
David Jackson
That’s a great idea, Alex!
David Jackson
i often bookmark sites when they’ve got either a nice lay-out or a interesting gadget (or something like that). cause it’s interesting what other websites look like, and what skills the webmasters of those site have. i don’t know all of the languages, so i like to discover new posibilities
Content of revisiting or consistent usefulness is the main reason why people bookmark websites (as in it’s so valuable they don’t want to risk forgetting about it).
PS: Most of my bookmarks are of projects I’m involved in (so I can easily manage all of my accounts and do my job effectively). 
Normally things that I think I’m likely to need or want to re-read in the near future. These normally fall under the categories of processing photos, taking better pictures, solutions to things I’ve realised I do that are bad coding practice (or an improvement) and generally cool or new web dev related things, especially javascript.
When I applied for jobs a couple of years ago I also bookmarked places that interested me.
I generally book mark sites depending upon the importance of the content it have. I am not minding other things.
These are some great replies, guys. Keep 'em coming!
David Jackson
If it’s interesting, but not quite necessary to subscribe to RSS (or the ability to unavailable) , or if it is something which is easily definable and classifiable, then it’s bookmarked. If it’s something transient and tag-able (say if I like a blg post about wordpress hacks) then I’ll use delicious. If it’s something of an area I’ll return to (say, like places of interest to visit) then I’ll usually use my native browser bookmarks.
bookmarks the link 
Most of my bookmarks are actually to basic designless websites with good physics/maths content on.
Design is useful but isn’t a reason for people to come back to your website unless they are designers themselves. It’s like having a restaurant - even if it looks nice, if the food is bad they won’t come back. If it looks boring but the food is great, it can still thrive.
FireFox has an excellent add-on for this purpose: Read it later
I use CTRL-D in Firefox almost subconsciously. If something reaches an “significance threshold” i will bookmark it.
That said, I can’t stand the Firefox bookmarking system (or any built in browser solution for that matter). Perhaps it’s because of the sheer volume of bookmarks, but I’ve never found a decent bookmarking management solution.
I bookmark articles with either tutorials (if I’m learning a certain topic like Apache mod_rewrite or Javascript) or articles for reference. Many of my bookmarks are so I can grab them for other people talking about the same subject. I also have my validators bookmarked because I’m too lazy to google. Some specs are bookmarked for quick lookups.
Because I don’t use RSS, I have a list of web comics bookmarked and I just check them every week.
RSS may be why some pages don’t get bookmarked as much as you would expect.
i almost never bookmark anymore, except if the site loads fresh articles often that i find interesting, or if they have great tutorials
I mostly bookmark websites when I’m in a hurry and don’t have the time to read all the content, so I can read it later on.
If there is lots of content I need later on, or too much interesting things to read and I still need it, I put it in my bookmarks.
Sometimes, to remind me, I just mail myself an email with a link to the website, so I can reach my deadline to read the info I need.
Documentation is often bookmarked or for IE users “favourited”. Prefer to download documentation though.
Anything that I’ll need to go back and look at for one reason or another.
Many webpages contain read-once content - i.e. once you’ve read it, you’ve read it and you know it. These don’t get bookmarked all too often.
Pages which have a lot of information (such as a reference) or which update regularly with useful information (such as a parcel tracking service) end up being bookmarked by me. I have a few dozen guitar tabs bookmarked, as well as some piano scores, some revision websites and a page which is currently tracking my soon-to-be-arriving laptop delivery.
I also bookmark services - such as quick translators (e.g. English to Welsh, or Decimal to Binary), RegEx checkers and email systems like Windows Live Mail. My phone has Facebook and Sky News bookmarked because they are the services I use most on my phone.
I always like to bookmark the website which are related to my theme and with full of unique information and great content.