@Nity:
Interesting article. "In a properly designed PC case, the fans create a ducted airflow that enters in the front, passes over the CPU, power supply and other heat-producing hardware". True, but many cases have pretty bad airflow over the graphics card (which can also be seen on the schematics in the article).
Are you sure he has a "properly designed PC case" WITH a good airflow over the PCI-ports?
if ((heat problem) && !(computer full of dust)) {
// he doesn't
}
Here is an example from corsair support forum which supports my theory...
http://forum.corsair.com/v3/showthread.php?t=86159"but when I switched to a 5970, I found that it was starved for air. (A simple test is to remove the door and see it if drastically changes things.)"
and
"...when I would remove the side panel my GPU temps would drop 7-8c"

/ Pimp