Well, I put it on my test system to see how it looks. I didn't see any improvements in video quality with the samples they provided over what could be done with divx or xvid. As for the audio, I'm not the best judge since I'm nearly deaf in one ear. The worst part is that WMP 6.4 won't download the new codecs, so once sites switch to the Media Player 9 codec, you won't be able to use the only good media player MS has made. Also, it doesn't include an uninstall option, which for beta software is not a very good idea.
Steve