I have Ubuntu 12.04 on an ASUS A53z laptop with Radeon HD6520G Video. My brightness keys work, but the brightness is always maxed on boot and I've been looking for a solution for a while. Setting the brightness at boot manually can get tiresome.
I found a small program called xbacklight that works on my system. It might not work on yours, but its worth a try. It uses percentage values, i.e. 20 = 20% brightness, and it does have a man page. If its not already installed on the system you can get it through apt get or synaptic.
Run the program in a terminal with no command line and it will report the current brightness setting as a percentage. xbacklight -set 50, will set 50% brightness.
If the program works for you, put it in the Startup Applications and it will run at each boot.