Raid 10 ftw 
Definitely setup a front-end and back-end machine. A killer all-in-one box is going to be annoyingly loud when your trying to watch a movie or even just trying to think.
MythTV > *
I’ve been using XBMC for months now and absolutely love it. Amazing interface and it can do just about anything. It really is a great option.
It doesn’t support full 1080p BluRay rips does it? I didn’t think it has the support to process that type of video and doesn’t have any digital outputs does it?
it didn’t a while ago but they may have codecs for them now… i don’t know i gave up on MCE a while ago because it was so bad, they certainly could have made it better by now.