My laptop screen is sometimes not bright enough and I have reach the top of the brightness according to the brightness control that is on the keyboard. The gnome applet brightness control has never worked either.
But today I’ve found an utility (which was on all my previous linux distrib, I guess) : xgamma.
Now I can adjust my brightness with this command:
xgamma -gamma 1.4
1.4 is a number between 0.100 and 10.000, default value is 1.
To make this modification permanent, you have to add a line to Monitor section of xorg configuration file (/etc/X11/xorg.conf) :
with your correct value instead of this 1.04.