I just got an invitation to join Twitter. Who is a member? What are the pluses and minuses of Tweeting?

This person is unknown to me, but claims they want to “follow” me on Twitter. As I understand it, part of the fascination is to see how much celebrity you can generate—how many Twits you can get floowing you whether they actually know you or not. How much time does Tweeting soak up. In what ways does it pay back for the effort?