70% of Twitter users joined in 2008

"70% of Twitter users joined in 2008
An estimated 5-10 thousand new accounts are opened per day
35% of Twitter users have 10 or fewer followers
9% of Twitter users follow no one at all
There is a strong correlation between the number of followers you have and the number of
people you follow"
Source: State of the Twittersphere Q4 2008 (page 2), produced by Hubspot.com