I opted to "explore" facebook, although I really already had an established facebook account. My account lets me everything that Twitter does, plus much more. Like Twitter, you can update your "profile status", letting the world know what you're up to, or where you are; unlike Twitter, however, you can upload photos, create extensive notes, join "groups", add applications, utilize a facebook IM chat client, and much, much more. For instance, I've also signed up to use another Web 2.0 service, Last.fm (a music streaming and tagging site that allows people to "broadcast" and share info about what music they're listening to currently, as well as bios on the groups/musicians, etc.). With a facebook/Last.fm shared application, I can share the music that I'm listening to through the Last.fm software, and have this info appear on my facebook profile pages. Total integration! I confess that I am a stalwart facebook addict, and need to temper my time spent on this social networking site with actual physical activity/movement, but alas, it is a useful, if somewhat all-consuming, tool for individuals and organizations alike.
http://www.facebook.com