I just tried the latest release of XBMC on OS X (0.1.1) today. Coming along very, very well. This release seems to be solid as can be. It supports the mouse now and in my 10 minutes of testing, worked great!
I'm thinking about moving my Mac Mini into the living room now.
I still find it hard to find good content in HD though. Most of the stuff says HDTV, but its only taken from HDTV, it isn't HD itself. Even when I do find an HD rip though, it rarely has the higher quality sound with it. I guess I'll have to wait awhile longer before I can finally throw away my Cable and Satellite boxes.