I've read so many conflicting things here and other places about this. Maybe somebody has figured this out...
According to Apple's posted specs, AirPlay should be supported on my early 2011 MBP (I checked the serial against the date) on Mountain Lion, but I can only get content through iTunes to play on my Apple TV 2nd gen. The Airplay icon appears on the MBP and seems to behave properly, but if I try to mirror my desktop to Apple TV it's just a black screen on the ATV. Audio seems to work fine. I even replaced my D-Link router with an Airport Express and no luck.
AirPlay from my iPhone 5 and iPad 2 to my Apple TV work perfectly.
Anybody with similar equipment able to get this to work, and if so, could you share your method?