It's a very limited device, with almost zero openness. Walled garden references are actually applicable correctly for once.
If you use Apple/ipads and itunes/iphoto, it almost makes sense, but even then, the connectivity to your itunes library is only one way - if you purchase a video on Apple TV, you still need to re-download it on your itunes. Airplay is Apple-only, and frankly, I don't see the point. All the internet features (eg youtube) are now available directly from most modern TV's or set-top boxes (inc Blu-ray), so no value-add there either.
Until Apple & itunes gets with the program (specifically the DNLA program, for one, plays more media types another), this is a very limited device.
Hasn't stopped it selling out here (Germany/Swiss border) in all the main tech stores before Xmas. Twice.
Caveat: I got one as a present. I'm *this close* from punting it on ebay...but for now, it stays connected, so it must be doing something right. Or maybe it's still novel.