If you’re running Ubuntu 10.10 or 11.04 on laptop, you might get a problem that fn key combination to change screen brightness is not working. Here’s a solution for nvidia laptop with this problem:
First edit xorg.conf in terminal with the command:
sudo gedit /etc/X11/xorg.conf
And then find the Section “Device” and add the bold line.
Identifier “Default Device”
Option “NoLogo” “True”
Option “RegistryDwords” “EnableBrightnessControl=1″
And now your brightness control is working in next login!
Thanks to Guskuma who posted it on http://ubuntuforums.org/showthread.php?t=1751333&page=2