Previewed at WWDC, launching in the fall.
Buy Movies Directly from Apple TV
Prior to this, the Apple TV could only be used to rent movies, not buy them. Instead, the customer would have to buy the movie on their computer and stream/sync it to their Apple TV. With the quiet addition of the "Buy" button, customers can instead buy movies directly from the Apple TV, which will later sync it back to your iTunes library. This had been a curious omission given that television shows and music could be purchased directly on the Apple TV.
It appears there was a glitch last month that caused the "Buy" option to appear briefly before Apple removed it.