I have installed Mint 13 KDE 64bit on a Samsung laptop. The hot buttons do not work for adjusting screen brightness. I searched for a widget; but the only one I could find was an Nvidia-type one. It did not work (although the laptop has Nvidia Optimus ).
I had previously installed Mint 13 XFCE on this machine, and managed to find a widget to adjust screen brightness. But I prefer KDE; so when this new version came out I installed it.
So it seems a bit odd that there is one for XFCE but not KDE. Even odder when considering how many widgets there are for, what seems like, the most obscure purposes.