Angry Birds has just launched on Facebook, and developer Rovio is trying out a different business model that flocks together with other freemium games on the social network. Rather than make you pay $1 up front for a mobile download, there's 4 new powerups that you can buy for cheap - just $1 for 20 uses. By expanding its in-app purchases beyond the level-beating Mighty Eagle, Rovio could earn higher a higher average lifetime revenue per user for itself and Facebook rather than squeezing a single golden egg from players upon install.