AirPlay for 3rd Party apps
According to John Gruber, this is not possible, unfortunately:


  AirPlay is the killer feature for Apple TV. But perhaps we’d better keep that in the future tense for now: it’s going to be the killer feature for Apple TV. After installing today’s various software updates for iOS devices, the only apps I’ve seen where AirPlay works for video are the built-in iPod app (a.k.a. “Video” on the iPad and iPod Touch) and YouTube. In other apps, AirPlay is audio-only.