It's a slow process so far, because it's too late in the game to jump ship for this season. It's practically August.
Depth charts have largely been set, you have to come in, learn a new system, get acclimated, etc. Not to mention, these kids have to uproot their lives and move to a new place, all within a couple of weeks before classes start. It's not a lot of time left to get a lot of things done. This isnt NCAA Football '13 where you can just plop these guys into a depth chart.
I don't expect many seniors, if any, to leave this year.. I think you will see some freshman leave now. Most of the kids who are going to move are going to play this season, and carefully plan their move for 2013.