If you've been waiting for XBMC media centre to finally be available for the latest jailbroken Apple TV 2 running version 5.2 (iOS 6.1), you no longer have to wait. You can now install XBMC with the latest stable update.
XBMC offers instructions on how to do the install on its wiki. You just need to enter a few commands in the command line, reboot, and you'll have that kickass, open-source media centre running on your Apple TV 2. Unfortunately, ATV3 owners, your Apple TV still isn't supported.
In case you missed it, you can see what's new in the Frodo 12 release, which this update was built upon, here.