Is Twitter lost on me?
chollida1: I'd put a third category of people in your list.There are people who have a lot of followers due to them having some form of celebrity.  People like Jeff Atwood have talked about how due to their large number of followers they are able to get very high quality answers to questions that they have.For some one just joining Twitter who doesn't have a "name" in the industry this type of question and answer usage is alot less useful.