Del.icio.us

I like the sharing aspect of using del.icio.us. Not only are you able to see what links others are using, but see what they're about. I think that the ability to tag makes some of the links more understandable. You can also see the frequency of tag usage through the tag cloud for the link, users' comments about the URL, and when the last additions were made to del.icio.us.

But what I really like is that you can set up a del.icio.us account and be able to import & access your favorites from any PC. This can be a real help when you're doing reference and can't get to the PC where you originally stored your Favorites.