Description: the nvidia 285.05.09 drivers are broken on NV40 hardware (at least) with respect to dpms and resume-from-ram.
(Performance-levels and clocking work as expected though)

Upon resume, screen is backlit but blank/black
. no information in /var/log/{dmesg,everything}.log
. no useful information in pm-suspend log
. hardware (below) not in any quirks database, so video99 not run
. tested pm-suspend with all the different video quirks options anyway, no luck
. no blacklisted hooks
. verified acpid is working by viewing acpi events from acpi_listen
. only Xorg.0.log error is "(EE) NVIDIA(GPU-0): Failed to determine output resource properties." however I believe that is an old message

managing dpms via "xset dpms force on/off" leads to either
. ~80% - no effect (aside from a flicker)
. ~20% - screen blank/black but backlit
. no error messages anywhere

Definitely a driver bug, not an X bug. See the error matrix:
nvidia 285.05.09-1 xorg-server 1.11.1-2 broken (dpms/resume)
nvidia 280.13-1 xorg-server 1.11.1-2 works (dpms/resume) warning about unsupported X ABI (nvidia driver but forced low-res)
nvidia 280.13-1 xorg-server 1.10.4-1 works (dpms/resume) ugly fonts like nouveau :-}
nvidia 285.05.09-1 xorg-server 1.10.4-1 broken (dpms/resume)

Hardware:
Dell E1705 (9400)
NV49(G71) Quadro FX 2500M

Additional info:
* package version(s)
extra/nvidia 285.05.09-1
extra/nvidia-utils 285.05.09-1

Right, it's broken. So what can possibly be done?