9.0 release hang in quiescent X

[Gary Aitken]

I've been struggling trying to ignore something and it refuses to go away :-(.

Running 9.0 release on an amd 64 box, standard kernel, 16GB, SSD (/, /usr, /var, /tmp) + HDDs, visiontek 900331 graphics card (ati radeon hd5550).  

As long as I am using the system, things seem to be fine.  However, when I leave the system idle for an extended period of time (e.g. overnight, out for the day, etc.), it often refuses to return from whatever state it is in.  The screen is blank and in standby for power saving, and <ctl><alt> Fn won't get me a console prompt.  The only way I know to recover is to power off and reboot.

When this first happened, the file systems would come up trashed and I needed to manually fsck everything.  I've gotten in the habit of doing a sync prior to leaving the system, and they now seem to come up clean when I have to reboot, but that's obviously not a solution to the problem.

Xorg.0.log shows the following errors:
  (EE) RADEON(0): Acceleration initialization failed
However, the display works fine and I'm assuming I'm just getting slow rendering, which is ok in this case.

Can someone suggest a good way to proceed to figure out what's going on?

Gary