An interesting tidbit has been uncovered in the iOS 5 beta relating to HD video playback. It appears that iDevices will finally be able to playback HD video at a full, 1080p resolution.
Specifically, the iPad 2 has been confirmed to have the ability to playback full, 1080p video in the Videos app. In the past, iTunes wouldn't even allow the syncing of 1080p video to an iDevice.