I have two Apple TV2 units. I downloaded this within hours of its appearance. It installed flawlessly, the first time, on both Apple TVs. (Previously, older editions would install on one but never the other.) I used the USB cable that came with my Harmony 650 remote, FWIW.
XBMC, at least as of May 25, 2012, would install via apt-get from the repositories, but did not display in the interface. A bit of googling turned up a patched deb package that could be installed with dpkg -i, so now I have xbmc.
I haven't had this version going long enough to detect stability problems, but previously, this would cause ATV2 to freeze up about once per week, requiring a reboot. It got to be a significant annoyance.
It helps to be able to use the command-line to ssh into the box directly, install wget, and download things like xbmc add-ons directly to the box.
Overall, considering what this is, and what you pay for it (it is free), it is a remarkable achievement. If you don't sort of enjoy software tinkering, however, this probably isn't going to impress you much. The modifications you can install are still quite limited. (I tried installing a VNC server. Although it works, it is so impossibly unresponsive, even with only 256 colors, that I decided to remove it. That's too bad, because I would really like a way to control my ATV2 from my laptop (one of mine is for music, and runs screen less).)