At 4:12 ET today Apple updated its AppleTV firmware.  It should be hitting devices shortly or can be downloaded for fun below.  There is no update list as of yet.

AppleTV(2G) (AppleTV2,1) 4.2.1 (8C154) 12/14/2010 16:12:02

Update: According to Apple’s release notes the update resolves an issue regarding 480p playback as well as a video re-downloading issue.

Feature Summary
TV resolution fix Addresses an issue that causes some high-definition TVs to incorrectly display at 480p.
Download fix Addresses an issue that may cause a movie or TV show to be re-downloaded.

Thanks for the image Doug!