I do use Twitter, but I'm a bigger fan of Plurk. You get karma points for relevant and interesting posts, and your Karma points can be used for fun decorations, badges, and avatars. Also, posts are shown in a nifty timelines which I feel gives me a better picture of what's going on than Twitter's boxy design.
I'm also a huge fan of MyLot. MyLot is a website of different groupings of forums, similar to Yahoo! Answers, except that you get paid for participating. That's right, paid just for making posts and replying to threads. Sure, it's just a couple cents per post, but if you spend an hour or so on there each day (and I do), it's easy to make $20 or $30 a month. Which is nice =)
And of course, Blogger. I love making friends, following blogs I enjoy, and getting comments from those who enjoy my blog! =)