Product Link:
PS3 Slim Cooling Fan (PS3)Do not buy this product. Firstly the clips that are supposed to hold it onto the PS3 only engage properly at one side. This is sufficient to hold it on but clearly shows the product to be hastily thrown together and not very well tested.
When connected you can feel air being drawn out of the back of the PS3, but I struggled to detect any difference between this and the normal breeze that is generated by the PS3 itself. After a reasonable playing time the air coming out of the back was not discernably cooler than without the fan.
The one that I bought worked for around two weeks and then the bearings started to wear out, meaning that the fans screech and grind and stall for a while before getting going. (Just like cheap old fans in PCs used to do).
In short its a cheap nasty (and probably imported) rip off, (it's now being got rid of at half price in many places... make of that what you will) trading on people's bad overheating experiences with original "fat" ps3's. I have yet to find a solution that is better than pointing a desk fan at the front of the PS3, but clearly that's quite noisy.