I’ve been using del.icio.us a ton lately. It’s one of those things that is easier to show than describe, but in short, it’s a community bookmarking system that features tagging in a Gmail-style way (meaning you can have a bookmark that falls under multiple classifications).
If their site can handle the bandwidth I think it’s really going to be huge. The idea is simple. You have an online system that keeps your bookmarks instead of holding the bookmarks on your physical hard drive. This means you’ve got access to your bookmarks from any internet-enabled computer. If you’re using a computer at work and bookmark a site with del.icio.us, it’ll be accessible from your home computer as well.
Even more powerful is the fact that almost everything in del.icio.us is RSS-enabled and works very well with Firefox’s livefeed system. For example, many people have a tag called "daily" which signifies a link they like to check on a daily basis. I’ve got fark.com, buzzflash.com, and a few others in my "daily" section. Now, you set your "daily" tag up as a live RSS bookmark in firefox. Let’s say you’re browsing a fantastic site at work (this site!) and want to mark it to be checked daily. You bookmark it with del.icio.us at work using the tag "daily", and through the magic of RSS, when you get home, there it is on your home machine in your "daily" bookmark.
That’s just a simple example but the ramifications and possibilities are tremendous. Here’s some other sites I’ve found that helped me make the most of del.icio.us:
Keep in mind this is a social/community bookmarking system, so it enables popular sites to sort of spread virally. You can also find out about a lot of interesting sites you never knew existing but are tremendously useful like this one or this one.
I’ve got a "popular" RSS bookmark in firefox that immediately links me to all the recent popular del.icio.us sites, and I’ve also got a bookmark feed that shows me things with specific tags to which I’ve subscribed.
Check it out. It’s very addictive.