Heh. Good question. My first reaction was that's like asking why I have a telephone. Those are just means of staying in touch with people, updated for the electronic age.

But, I guess more accurately, it combines two big parts of my personality -- I'm pretty social, and I'm a writer. I have no desire to use Facebook to play Farmville or anything; I use it to interact with, to communicate with, friends. And take formspring, for example. I enjoy thinking about and coming up with responses to the questions, and I love that the site lets me involve friends in that. My blog is largely where I work through stuff that's on my mind, but do it in a way where it can be a conversation instead of just in my head. Twitter is purely me being neurotic -- I'm spoiled on being able to share what's on my mind, and when I don't have another outlet for that, I can broadcast it into the ether on Twitter.