Well We are now around to Ubutu Lucid Lynx (10.04) and it looks like nothing has changed support wise, so to get the backlight to adjust, just add:
to the “GRUB_CMDLINE_LINUX_DEFAULT” section, right after “quiet splash” and before the closing quotation mark. Now run
and you will be good to go! Reboot and try out your freshly brewed screen backlight adjustments!