I use Twitter in a very different way than Facebook though, and for very different reasons. I follow a small group of smart, funny or creative people that tweet really interesting stuff, but personally I tweet only a few times a month. Am I alone in that I don't use Twitter as a social networking tool, and more of a broadcasting-listening tool?
To anyone looking at my twitter, it might seem extremely quiet and ghost-townish, but I am using Twitter much more than Facebook and getting more from it, albeit passively.