Apple has released Apple TV software version 2.3. AppleInsider reports that this update allows users to stream music from the Apple TV to other Apple TVs or AirPort Expresses. The update also allows users to use third party remotes with their Apple TV, which has been a long standing request from many users.
The Apple TV can now function the same way a computer would for those who use AirTunes to stream music throughout the house.
Being able to use remotes other than the Apple supplied remote has been a critical issue for many who want to integrate an Apple TV into an existing home theater setup. The ability to use third party remotes should allow the use of many of the popular remotes currently available.
If you have an Apple TV, I would recommend updating. The update is available directly from the built-in updater on the Apple TV.