When I press the Fn+F5 or Fn+F6, the sliders goes up or down, but the brightness won't change. I had the same issue on the Lucid Lynx, but I could fix adding ”quiet acpi_osi=Linux acpi_backlight=vendor splash” to the "GRUB_CMDLINE_LINUX=".
But on the 11.10, this solution won't work. If I try this workaround, the brightness slider stop working (show either maximum brigthness or minimum, but no change). If I add only "acpi_osi=Linux" the slider works, but still no change.
I'm desperate for a solution now, it's been months looking for it and it's really difficult to use the laptop with maximum brightness all-time. Some distros like OpenSUSE works fine, but I hate 'em.
Motherboard: Pegatron H24Z BIOS: American Megatrends 200.T67 Intel Core2Duo T6600 2GB RAM HD 500GB Brand: Positivo SIM+ (Brazillian PC-maker)