(In reply to comment #10)
> Is this still an issue with a newer kernel?  Did you also update your
> userspace stack (mesa, xf86-video-ati)?

The bug seems to have nothing to do with the actual two X server configuration
and the used window manager/desktop combination.

Last night we started an Ubuntu 12.04.3 Live CD session with kernel 3.8, whose
700 MB disk space just provide a simple standard one X server desktop (Unity,
compiz, gdm). We experienced a few short (about half a second) black screens
(GPU resets?) and after about 10 min. a kernel freeze with striped screen.

Unfortunately, the Ubuntu Live CD does not come with a netconsole, so we have
no logs.