iPhoneDevCamp did an interesting thing with twitter. They created an account: http://twitter.com/iphonedevcamp Then, they ran a script that would automatically add each person as a friend when you added them.
The goal of Twitter is to tweet to the people who are your friends. You may show up on the public timeline, but it's not so much a marketing device as it is a way to say.. I'm hanging out at Cafe Lo Cubano.. anybody want to go see a movie?
iPhoneDevCamp's implementation allowed any comment made to the that account be distributed to the entire group as Twitter would send an email if you have that as your preference for receiving updates.