Apple has just released a new update for the generation 2 and 3 Apple TV models. The update allows movies and TV show previews from the iTunes Store to be viewed in HD and fixes a few other minor issues.

Apple TV Software Update 5.0.1

iTunes previews – Previews for movies and TV shows from the iTunes Store can now be viewed in HD.
AirPlay – Fixes an issue that caused some iOS apps to have trouble connecting via AirPlay.
Home Sharing – Improves the reliability of Home Sharing connections.
Netflix – Addresses an issue affecting Netflix login and navigation.
Stability and performance – Includes fixes for issues affecting stability and performance.

Source [macrumors]