The title says it all, Rovio's Angry Birds game has reached over 10 million Monthly Active Users on Facebook's gaming platform. The game launched less than a month ago on Valentines day, meaning this Facebook metric currently tabs up the the number of unique users since its launch. As of this writing, the total number of uniques are around 10.2 million MAU, with another 1.1 million users added today according to the independent Facebook apps metrics webiste, App Data.
This growth can likely be attributed to the ability of the Facebook app to easily reach users who don't have a smartphone, and due to the social hooks that Rovio has taken advantage of. When playing the game, its easy to invite your friends and see how you stand up next to your friends who have also played the same level. You can also "brag" to your fiends about the score you've gotten, and Facebook posts the points you've scored on your wall.
While somewhat unsurprising, this growth is still remarkable.