Mostly it's just to keep my daily bookmarks organized and available from multiple workstations (I hate missing my comics on the weekend because I don't have them bookmarked on the home machine).
I'm not sure I like it, though. Any of you use del.icio.us? Besides giving you server-side storage of bookmarks (something I have as part of my website, actually), what does it do for you? How do you keep it from turning into a great big tar-baby of links that is impossible to use?