research from Yahoo suggests that most Twitter accounts are not used
The figures show that found that only 20,000 people are pretty much responsible for half of all tweets. This is less than one percent which suggests most people sign up and don't say anything.
The study only analysed a sample of 260 million tweets. Half of those tweets came from “elite” users, consisting of “media, celebrities, organizations and bloggers.”
There are a few ordinary users who don't have a lot of followers but seem to spend their time following famous people. Apparently famous people like to follow famous people, and writers follow other writers.