I discovered post upgrade that Ubuntu 14.04 has a glaring bug with the Intel graphics card (which was working fine in 12.04), the Fn key no longer controlled the brightness.
sudo su
ls /sys/class/backlight
if it lists intel_backlight then this solution of adding the following should work for you too...
vi /usr/share/X11/xorg.conf.d/20-intel.conf
Section "Device"
Identifier "card0"
Driver "intel"
Option "Backlight" "intel_backlight"
BusID "PCI:0:2:0"
EndSection
Log out and log back in, function keys should now control the brightness again (no more glaring bug!)