I'm writing this from my Athlon 64 X2 computer where I've just installed RC1.7. No problems so far. I installed the proprietary ATI driver and it's working, in contrast to my other desktop with a Radeon 9200, where any attempt to build the proprietary driver with VASM generates an error and doesn't work. Maybe the Radeon 9200 is too old for that driver. When 5.9 goes Gold I'll try building the Radeon driver from the proper download for the Radeon 9200 from ATI's Web site.
I do occasionally get minor artifacts onscreen with the Athlon 64. Not enough to be concerned with, but something must be not quite right.
Audacious is playing both WMAs and MP3s when I run it as user. My Celeron desktop and Turion 64 laptop don't play MP3s as user. The sound in the Athlon desktop is given in lspci as Multimedia audio controller: ATI Technologies Inc IXP SB400 AC'97 Audio Controller (rev 02).
Nothing else to report yet. So far this computer seems extremely happy with RC1.7.
I'm extremely happy with RC1.7, too.
Am really looking forward to the final release.