I wouldn't download them if i had the choice. Xbox only plays the stuff with all the advanced profiling turned off, and then its comparable to xvid without that edge.
At lower bitrates it easily pawns xvid in the examples i've seen, higher the bitrate though the less convincing/disctictly better it is (it edges it in some tests). Yet its the fact that xvid requires lower resources at the high bitrate kind of seals the xvid deal for me. If it wasn't so poor on the compatability and resource usage front it would esaily be a viable, and in fact likely, choice for me
I have used it for HDTV stuff, simply because nothing but my pc plays that anyway so i might as well and i've gotten better results.