I had no problems with backlight when using samsung tools + nvidia-bl-dkms + "EnableBrightnessControl" in xorg.conf. But yesterday I uninstalled nvidia drivers because open source Nouveau driver looks better and better. It have 2D and 3D support so compiz effects can be use. I don't play games so it's good enough for me. I also feel that GNOME is faster. But the most important thing is that there are no problems with the second monitor and you can switch him with function key (don't work on nvidia drivers). Now all fn keys on my laptop works but brightness control fn key has stopped working after uninstall nvidia drivers. Xorg.conf file disappear, I can't use nvidia-bl-dkms anymore and samsung-backlight is for intel. So how activate brightness control? When I change brightness, notification is showing but progress can't change. "echo 80 > brightness" in /proc/acpi/video/NVID/LCD works fine. I read that Nouveau should handle brightness control and I remember when I had clear ubuntu installation it worked.