Im really looking forward to this as I have two original xboxes running xbmc and they are both starting to fail now.
My xbox 360 has never been online so still have the old dashboard however from what Ive read its not going to be a simple software update to get homebrew running and if thats the case I wont bother.
I tried PS3 linux and wasnt impressed. Got a Megadrive emulator running but it wasnt full speed so gave up on it. I now play Mame etc.. on my PC with a 360 usb pad and its great.