I swear I read there was some XBMC-clone out for the PS3 and it was quite capable of playing 1080p video. I just looked again, and can't find any reference to it. Did I dream it? Weird...
The closest thing I can find is MegaBox, which was apparently in the news in January 2008 and never mentioned again. It seems to have disappeared (or perhaps it was never real?).
The PS3 seems like the perfect platform for this app, I wonder why it hasn't been ported to it. There are similar apps already available. They're capable of playing 1080p video, and they can be used easily (just burn a DVD, no need to even install anything) and legally, with no hackery (like you have to do with the original XBMC). Those apps just aren't nearly as slick as Boxee, or even XBMC.