Apple has released iOS 5.1 for Apple TV 2G and Apple TV 3G, which includes support for shared photo streams, search for movie trailers, switch between different iTunes accounts, and adds some stability and performance improvements.
Screen savers: New Cascade, Shrinking Tiles, and Sliding Panels screen savers.
Main menu: Reorder icons on the second page by holding down the select button on the remote.
Subtitles: SDH support for the deaf and hard-of-hearing as well as improvements to viewing and selecting subtitles.
Network configuration: Support for setting up advanced network options using configuration profiles. See http://support.apple.com/kb/HT5437 for more information.