I bought one on a whim, and it’s really great! Especially if you jailbreak it and add nitrotv and firecore flashblack. It adds the ability to have non iTunes media players like plex, xbmc, and mplayer. Also vnc, last.fm, an Internet browser with flash, ssh, and 3rd party remote apps. But even if you don’t jailbreak, AirPlay alone is a feature worth the $99 price.
And there are other ways around the iTunes only content without jailbreaking. Such as the stream2me iPhone app that streams all media from your pc to your iPhone, which then an be streamed to your apple tv via AirPlay.