I have this now as part of the alpha and am testing it out on a Macbook Pro. This is going to be the killer HTPC in my opinion. They have basically taken the powerful features of XBMC and thrown a VERY sweet front end on it. UI is subjective but to me it's much cleaner and nicer looking and working now. It's alpha so there are bugs, etc, but it is very promising. Try to get onto the alpha test: www.boxee.tv
They are also releasing alpha for Linux so this could be eventually ported to non-Mac hardware down the road. The way this looks from my early tests has me thinking about possibly changing away from Vista MCE on my main HTPC hooked to the projector. And I really like Vista MCE/MyMovies.