Study conducted by Harvard business shows 10% of users generate 90% of the content.

http://blogs.harvardbusiness.org/cs/2009/06/new_twitter_research_men_follo.html 

It would be nice to intersect this data with are the top 10% Companies pushing out data making it monologue and not 2-way peer-to-peer communication which in the end is the purpose of twitter.