I'm running Linux Mint 13 stock with Cinnamon on a Lenovo ThinkPad W520 4276-39U laptop with an NVIDIA Quadro M1000 GF108GL (NVIDIA driver version 295.40). The Fn+Home and Fn+End (LED brightness increase and decrease, respectively), works when in consoles; however, in Cinnamon, they don't. When those keys are clicked, the brightness slider pops up and indicates changes, though brightness doesn't change. Also, the software brightness control, under Cinnamon Settings: Brightness and Lock, also has no effect.
Not sure if it's relevant, though, while trying to work through the issue, I switched the kernel from acpi_backlight=vendor (implicit default) to acpi_backlight=thinkpad_acpi. When operating under that driver, Fn+Home and Fn+End poped the brightness slider up, yet no change was indicated (and no change occurred). Also, under that driver, unhandled HKEY events were sent to syslog. Since then, I've restored the default configuration.
Any assistance would be appreciated.