ubuntu 11.10 brightness doesn't work

First back up:

sudo cp /etc/X11/xorg.conf /etc/X11/xorg.backup

Then:

sudo gedit /etc/X11/xorg.conf

Find the "Option "No Logo" " Add this underneath:

Option "RegistryDwords" "EnableBrightnessControl=1"   

(Including all the quotes)

Then save either restart. That should work but you may need to edit grub, try the above first.