Comment 13 for bug 743352

I suggest finding a temporary setup where the backlight control works, in which the nvidia driver is not installed, and then looking at "lsmod | grep _bl" or the contents of /sys/class/backlight/ which should hint at the module name that controls it. We can't blame the nvidia driver if the backlight has never worked under any Linux on the machine (though that appears to be the problem on my MBA 3,1).

Also, you need to exclude the possibility that maybe your Macbook Pro hardware is still too new to be fully recognized by the 2.6.38 kernel in natty. So if you can't find a test setup above in which the backlight control ever works, please try temporarily installing the latest mainline kernel:
    http://kernel.ubuntu.com/~kernel-ppa/mainline/v2.6.39-rc4-natty/ (linux-image-*.deb)
I notice there have been a couple of commits to the apple_bl (formerly mbp_nvidia_bl) module in those recent kernels.