http://www.xoxide.com/sunbeam-transformer-case-black.html
This link will show you one of the coolest running cases out today. Intake is at the bottom and exhaust at top (heat rises). Pwr supply will exit hot air out back of case. Side fans also exit air from case. It is loud and I use a fan controler to reduce noise and cable clutter.
I'm not sure, but I think the answer depends on the case and where the drives are mounted. I think you can try a little experiment by doing it both ways- try measuring the temperature when the air moving out vs. air moving in and see. Let me know the results if you do decide to try!
I have been searching online to finally find out which direction to place case fans. I have found two different answers on the top (lid) of the case. One place says to have the air enter the case and the other says to have the air exit the case. This was with a fan in front, bringing air in. Then a fan below the powersupply pulling air out. SO WHICH DIRECTION DO I HAVE THE AIR MOVING ON THE TOP OF THE CASE.
Also some case manufacturers have a spot on the side of the case for a fan.
I have heard that too many fans are no good and not enough or fans working against each other are also bad.
Does the exhaust fan below the power supply (not the power supply fan), cause problems with the cpu fan?
Please clear the air on this subject if you would. And thanks for any help. 
