I just installed it this weekend. It's fantastic. My wife, who was skeptical and rolled her eyes every time I said I was going to fix an old xbox and make it out media center, is totally "sold" to use her word.
I'm still exploring features and learning the ins & outs, but we love it. Best $15 I ever spent (for Splinter Cell to do the softmod).
A couple of questions if NE1 wants to answer:
Some people in this thread said they canceled cableTV or DirecTV now that they have XBMC... why? Are you able to get full network TV streams via XBMC?
@ 6stringkng: What's "XD"?