In an interesting academic study titled: Pulse of the Nation: U.S. Mood Throughout the Day inferred from Twitter, researchers at Northeastern University and Harvard University, studied over 300 million tweets (Sep 2006 - Aug 2009) collected  represented as density-preserving cartograms (nice graphics). I view this research as an interesting exercise in how longitudinal Twitter research might be used to analyze B2B market perceptions and trends. The research itself yields some predictable results: people who live in California and Florida seem to be pretty happy (perhaps all that sunshine). Inferences that were interesting and unexpected: The highest "tweet mood score" was Sunday morning. The lowest, Thursday evening. The greatest number of happy tweets were in the early morning. BTW - This study was based on 300 million tweets over about a 3 year period. A recent estimate shows that there are now around 2 billion tweets/month.