Sorry if I'm trolling a bit here, but from what I heard besides the fact Boxee makes Apple TV actually useful, there is an 800lbs gorilla in the room - Apple TV's processor is too weak to handle HD video, otherwise its same as desktop/boxee box platform. Boxee is very promising application, unfortunately still has some rough corners and intended limitations (like Lack of BD playback in any shape or form (MKV is fine thou).
ps: I also belive since engadget wrote this article Boxee Beta has become available for all platforms including Apple TV