Since June 1, 2009 there has been 282,536 tweets. Upon visiting this site, you will see the counter is going up so fast. They have a search option where you can search for the game of your choice and see the tweets about it.
They also have a most talked about games section on the homepage. Currently leading with 64,134 tweets, is The Sims 3. In second place is WoW, but only with 13,051 tweets.
Check out Tweet My Gaming on twitter to follow all their updates.