Comment 7 for bug 551668

Got same bug, or at least closely related. nvidia GT216 [GeForce GT240M] does not respond to brightness commands.
This laptop is a new Fujitsu Amilo Pi 3560. The keys are Fn-F8(down); Fn-F9(up).

Attached Xorg.0.log shows events:

(II) May 10 20:29:32 NVIDIA(0): Setting mode
(II) May 10 20:29:32 NVIDIA(0): "CRT:nvidia-auto-select+0+0,DFP:nvidia-auto-select+0+0"
(II) May 10 20:29:33 NVIDIA(0): ACPI display change hotkey events enabled: the X server is new
(II) May 10 20:29:33 NVIDIA(0): enough to receive ACPI hotkey events.
(WW) May 10 20:29:33 NVIDIA(0): ACPI: Error: Unable to find the brightness file path under
(WW) May 10 20:29:33 NVIDIA(0): /proc/acpi/video. The NVIDIA X driver will not be able to
(WW) May 10 20:29:33 NVIDIA(0): respond to ACPI brightness change hotkey events.