Update 1: The support document is now available online.
Apple has just released an update for the second generation Apple TV. iOS 4.2.2 is build 8F305 and most likely fixes bugs and has performance improvements, like previous updates.
If your Apple TV 2G is currently on an untethered jailbreak, MuscleNerd from the iPhone Dev Team has advised people to stay away from this update. A jailbroken Apple TV 2G has allowed for .AVI streaming to directly from my MacBook Pro right to Apple TV via XBMC.
For those not interested in the jailbreak anymore, the direct download link is here.