I just installed RC1 AMD64. I'm displeased with the "upgrade" as it appears to have wiped out my entire configuration even though the install found it and I selected the option to keep settings and /home. I had to go through the video wizard, which I expected, then it started taking me through the names, rooms, TV, cable, etc. etc. etc. Short of my videos which are on an external USB drive (and not hooked up during install), it appears to be a clean install. Admittedly, I didn't go into MythTV, I just checked the H.264 videos, saw that all my settings including my pain the butt remote are gone (fortunately setting up the remote was enough hassle that I posted a how-to with all the codes in case anyone else wanted to use the same remote, so that should be here on the forum). E-mail server (postfix) is gone, e-mail gone, dns setup gone, my networking settings with static IP gone (all my computers off the net until I could get that fixed), etc..
Anyway, I tried playing H.264 videos and the f'ing green blocks are still there. From KDE desktop both mplayer and xine play just fine, but from within LMCE the green blocks are killing it.
Time for a real test. I just kicked off a download of the i386 DVD and I'll be installing from scratch tomorrow or as soon as I get the DVD downloaded. IF I can get it loaded.. After 5 or 10 minutes it's still sitting at 0 Bytes downloaded.