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.

Section “Device”
Identifier “Default Device”
Option “NoLogo” “True”
Option “RegistryDwords” “EnableBrightnessControl=1″
EndSection

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