In some sense, twitter is IRC: you address @persons that meet on the same place you are, talking about some #topic. At one point I had the idea to actually writ

In some sense, twitter is IRC: you address @persons that meet on the same place you are, talking about some #topic. At one point I had the idea to actually write an IRC server where you would join a #channel that was actually a #topic, and the server would send you @people's tweets as messages. The usual guidelines for IM (putting @person's name before the message) would even be enough to reply to someone's tweet.