I have been using
del.icio.us for awhile now and just love it. Del.icio.us is a social bookmarking site; in other words, it is a service that allows you to save, keep track, and share bookmarks online. Having the ability to save bookmarks online on del.icio.us is really useful if you use computers at multiple locations, in that wherever you go, you still have access to them. On top of that once your bookmarks are online, you can share your bookmarks with others. You can also view what other people have bookmarked, how many
people have bookmarked a page, and search through all of the bookmarks on del.icio.us.
When saving bookmarks you can add metadata called "tags" to them. These tags help describe more about the particular bookmark. For example, I added
http://www.wikipedia.com as a bookmark to del.icio.us with the tags "encyclopedia", "research", and "reference". After using del.icio.us for awhile I have many bookmarks with these tags. Now when I click on my
reference tag, I can find all the other bookmarks that has "reference" as a tag. I can also see all the webpages that other people using del.icio.us tagged with "reference" as well as just the popular webpages with that tag. It's a great and fun way to discover new sites.
I find tagging really helpful in keeping track of my bookmarks. No longer am I constrained by the categorization of folders used in the browser's favorites menu. I am free to tag sites that I bookmark with the terms that I want. I can quickly find the sites I bookmark using these tags as well. For example, I can easily look for all the links I saved about ASP.NET 2.0 conversion by going through the links in "asp.net+conversion" like so,
http://del.icio.us/a7an/ASP.NET+conversion . There's also several ways to look at the tags.

One neat new concept is called a "Tag cloud". A tag cloud is a weighted list of the tags. More frequently used tags are depicted in a larger and bolder font. It makes finding tags you use often easily.
Some of the others cool things you can do is tag links for other people, sort tags into bundles, and syndicate tags through rss. There are firefox extensions for del.icio.us as well and you can use firefox live bookmarks with del.icio.us. I'll talk more about that maybe in other post.
Del.icio.us recently went through some growing pains with its popularity. It's slower than it was before, however don't let this stop you from trying it out and using it to store and tag your own bookmarks.