Looks like nVidia 196.75 drivers have faulty fan control software, this causes frame rates to drop while you are playing games or performing any other GPU intensive tasks, this is a result of overheating. It is recommended that if your using this version of the drivers that you revert to the previous version.
There have also been cases of video cards failing due to the overheating, god help anyone running Folding@Home.
nVidia Forum: