I had a problem with waking up out of sleep mode (S1 or S3) when using a nvidia 5200 fx video card. My 6800 worked fine in the same hardware so I knew it had to be video driver/hardware problem.
If MM_X_RESTART_ON_SLEEP_ENABLED='yes' and MM_ACPI_VIDEO_FLAGS='2' were enabled it wake up about 10% of the time, but most of the time it would just be a black screen other times X would crash complaining about a lack of video memory.
If MM_X_RESTART_ON_SLEEP_ENABLED='yes' was not set it would cause the X process to go to 99-100% cpu forever.
After much playing I found out the problem/workaround was as simple as adding:
Option "NvAGP" "0" to my xorg config. I didn't know how to do it from inside the minimyth.conf so I just made a copy of xorg.conf and enabled MM_X_FETCH_XORG_CONF='yes'
Don't know if this will help anyone but I figured I would post it anyways.