Your Apple TV has an update pending. You can move up to OS 5.1 by going to Settings > General > Update Software. Today's update adds support for Shared Photo Streams (a welcome new feature in iOS 6), but there's a lot more to love here.
Something I've always wanted was the ability to switch store accounts, so my kids can load up their purchases. Now you can. Some other niceties include being able to beam audio from the Apple TV elsewhere (good news to me, as I'd like to pump the Apple TV audio into an old Airport Express I have connected to a stereo system), new screen savers, subtitles, movie trailer search (with local showtimes), support for advanced network options using configuration profiles (using Configurator) plus the usual "stability and performance" updates.
Oh, and apparently you can re-order the icons on the main menu by holding down the select button on the remote. Now where'd they get that idea? And yes, the YouTube app is still there.