Twitter is a Web 2.0 platforms built around the need to always know what our friends doing, just like checking Facebook or instant messaging.
Users have 140 characters to answer the simple prompt: "What are you doing?" Responses, called "tweets," are instantly sent to your "followers"--Twitter's way of saying "friends"--who read them in their RSS-like Twitter feed or via SMS textalerts.
"It's the perfect platform for self promotion," says Forbes magazine.