Stumbled upon this last night! Using the iTeleport app and airplay mirroring, I airplayed my iMac screen to my aTV2, and the app turns into a touchpad/keyboard. Work perfect with 4S and iPad2. No reference for this feature anywhere I can find.
Tip: If you are already connected to the computer and start airplay, it will just mirror your iDevice, but if you start airplay mirroring then connect to the computer, the iTeleport spin logo will appear on the TV followed by the computer screen, and the iDevice becomes a controller.
Tip: If you are already connected to the computer and start airplay, it will just mirror your iDevice, but if you start airplay mirroring then connect to the computer, the iTeleport spin logo will appear on the TV followed by the computer screen, and the iDevice becomes a controller.