Usul's xorg.conf, another go...

What you know...
It's been a year or so, and the NVIDIA card (on the Thinkpad T410) has the same problem than while running Lucid Lynx.
The keyboard shortcut to lower or brighten the LCD doesn't work, it does launch the OSD icons for both up & down, but it doesn't actually do dink.
On the same laptop, with Lucid, it was necessary to do something similar.
Not a big deal.

Section "Device"
        Identifier      "Default Device"
        Driver          "nvidia"
        Option          "NoLogo"                "True"
        Option          "RegistryDwords"        "EnableBrightnessControl=1"
EndSection