I wanted to provide some resources, tutorials and links for those people who want to jailbreak a second generation apple tv (running 4.4.4 or lower) and install XBMC on it.
This solution has provided my family and me almost all our media entertainment for the last year at 1/4 the price of cable.
I may add additional information as I get feedback in order to give more details as people ask.
Using seasonpass to jailbreak atv2 (good tutorial with links to all you need are on the Firecore site) http://support.firecore.com/entries/387605
You may also decide to use ATV (black) from fire core, which costs about $15-30, but you don’t have to. It makes it uber-simple to install, but you can just ssh into your ATV to install the components you want- requires a bit more knowledge of terminal commands, but there are tutorials for that as well (see below)
ATV Flash (Black) 1.5 for iOS 5.0 is out from Firecore. The untethered jailbreak for ATV2 & ATV3 should be forthcoming anyday. In the meantime, a tethered jailbreak is out for ATV2 w/ iOS 5 (and , of course you can always just stay on iOS 4.4.4 & below until then) http://blog.firecore.com/