Why do you Twitter?

Here’s an honest question for everybody who has a Twitter feed on top of their regular blog: why do you do it? I feel like I’m missing something. If you have a phone that can update a Twitter feed, and you have a WordPress/Blogger/Livejournal blog, it’s relatively easy to just update the blog using the phone. The built-in webbrowser can do it. If you have an iPhone, there’s various (upcoming) apps that make it even easier. And the little bit of extra hassle to log in etc. sounds like a good filter to me to weed out everything that isn’t really post-worthy.

Which brings me back to the question: what am I missing? Is there some social component that I’m not aware of? Is Twitter turning out to be a fad and I just haven’t noticed it yet? Help me out!