Was recently stuck with a non functioning Fn key combination to increase or decrease the screen brightness.
Some people have generously added a gnome applet to do the trick.
Being the command line we like:
a simple custom built
kish@Griffin:~$ cat /usr/sbin/brightness
echo $1 |sudo tee /sys/devices/virtual/backlight/acpi_video0/brightness
It seems safe, need to dig deep to verify.
Tested on Karmic Koala