Heh. Got a side project that does exactly that (twitter-forum, NOT a chat room), and everyone that saw it first thought it was a (lousy) chat room.
I believe there is use in micro-forums (or group-twitters) different than chats; it's a group timeline, it's meant to be persistent, not real-time conversation (though faster than doing blog/forum posts) of group of people publishing related tidbits of information (or replying to / referencing it).
(Shameless plug, my project is http://speeka.net/ , one-tech-guy side project that's practically dormant atm because of lack of spare time and biz/marketing efforts).
A chat room?