Use the TwitterCounter API to retrieve all data stored in TwitterCounter for a particular Twitter username. TwitterCounter keeps stats about Twitter users, such as the most popular, top 10 lists, and so on. The API results include a user's avatar, number of followers, average follower growth, projected follower growth, followers two weeks ago, followers yesterday, and more.
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There are no source code libraries or how-to links for TwitterCounter. If you know one why not add it?
Good collection of Twitter stats.