Didn't try it on mine as the I have my fans is to create a vacuum affect to lessen noise, whilst giving good air flow.
But i did try it on an AMD2Ghz with an ECS motherboard
The motherboard temp reduced by 6 degrees. Didnt make any real difference to the chip.
Points to remember. Make sure the fan is not in oscilation mode.
If using a floor standing fan (I was). Be sure to balance the pc well & that it is stable (had to catch it).
Overall score out of 10
Temp reduction 8
Ease of use 0