I just finished the first ever "State of the Twittersphere" report using data on over 600,000 Twitter profiles from Twitter Grader (yes, it slowed down Excel a bit). There were a bunch of interesting trends, but the most surprising to me was that based on my estimates from looking at the data, Twitter seems to be growing by 5,000 to 10,000 new accounts per day.
See the full "State of the Twittersphere" report.
