I decided to limit myself to just a couple of hours of Apple TV hacking this morning as I have books that need writing, children who need feeding, a house that needs cleaning and, lord almighty, you wouldn't believe the laundry. So again, this is going to be a quick update rather than an in-depth exploration of all things Apple TV.
As you know, the 2nd gen iOS Apple TV has already been jailbroken. While tools have not yet been released, you can watch a video posted earlier today showing command line access to the unit.
I do not have jb access so have limited my explorations to the tools I have available. I used Kevin Ballard's superb Bonjour Browser to scan for Apple TV services. At this time, there appear to be two. First, there is the standard AirTunes "raop" service. RAOP stands for the remote audio output protocol, which has been used for some time with Airport audio streaming. There's a nice discussion of the protocol over at CocoaDev.