I mentioned earlier that I had been using my own Linux-based media center for a couple years now. Even then, my first impression with XBMC was complete astonishment. The system performance just crushes my Linux system's; I suspect this is mostly because XBMC doesn't have to deal with the overhead of a "real" operating system.
The user interface is so much more aesthetically pleasing than Freevo 1, although Freevo 2 looks great and should make for an interesting comparison down the road. One thing I do like about Freevo that (to my knowledge) XBMC doesn't offer, is a way to browse your movies by cover images.
I was a little skeptical that streaming media via SMB (Windows file sharing) would perform well since I had a hard time getting the performance to watchable levels in Linux. But I was pleasantly surprised! I was able to stream everything from Divx movies to MPEGs to MP3s and still images to XBMC. I ended up using NFS on my Linux-based media center in the end; Linux-to-Linux streaming just doesn't work as well with SMB.
XBMC is a very impressive project. Being able to run natively on the Xbox allows XBMC to take full advantage of the limited hardware available and really delivers a slick user experience. For around $100, plus a little time, you can convert your Xbox into a formidable media player that rivals systems with twice the hardware.