A large number of podcasters that I listen to have been talking a lot about Twitter.
When I first looked at it, I didn't really get it.
But I think a recent TWIT mentioned that it was kinda like a casual blog which peaked my interest ... somewhere in-between a blog post and a non-blog post.
It definitely could be used for keeping people in your close circle of online friends updated on what you are doing, where you are at, etc. Kinda like your IM setting for your status but with more details and updates.