Twitter recently announced that it hit 50 million tweets per day, averaging out to about 600 tweets per second. Back in 2007, users were only tweeting about 5,000 times per day. Last year, the number of tweets grew 1,400-percent to about 35 million tweets per day. These numbers display the microblogging website’s increasing popularity and exponential growth.
Source: Twitter blog; Monday, February 22, 2010