Unsurprisingly, 1/3 of these are generated by postbots
Before you say SPAM, check this:
Of the most active Twitter users updating more than 150 times/day, nearly all of them are bots operated by sources such as hotels offering deals, regional and national news services, regional weather services, the top news within Digg, games, anim services, tags within del.icio.us and financial aggregators. These very active bots account for one-quarter of all tweets.
Here's the report:
http://sysomos.com/insidetwitter/mostactiveusers/
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http://www.highrevenue.com/tag/twitter
