Unfortunately Apple TV plays at a maximum resolution of 720p. While technically this is HD, it is a long way from 1080p, and the limitations will show on a full resolution 50″ plasma. There are other digital media servers on the market that do play 1080p.
The other potential problem with a 50″ plasma is that the ideal viewing distance is around 12 feet. As you start to close that gap imperfections and pixellation will become more apparent. If the source media is already compressed to MPEG2 SD and then upressed using a domestic dvd player, you will battle to achieve a high quality image.
Ryan Spanger
Dream Engine