As of right now, I do not have a Twitter account. I am seriously thinking of experimenting with it in the next few weeks. There are several good books on Amazon regarding using Twitter for marketing purposes. I have several trials scheduled to start in the next few weeks. Depending on scheduling and such, I may give it a shot in a few weeks after doing a little more research.
Unrelated, it is also a good place to go discovery on cases of any kind. For some reason, I have noticed that people tend to tweet stuff they would never put on Facebook.