Depends on the case.
PYZCHOB!+C# being the full tower is it the following :-
1x Front on the bottom (sucking)
1x Side Panel (sucking). I modded this one so it would be close enough to being on top of the CPU.
2x Back (blowing)
SUPERSONICB!+C#'s case only has the one intake fan.
This fan is on the front behind the front USB and MultiMedia ports.
The problem with this case is that it has a smaller form factor. It's one of those case the PSU mounted sideways. I have noticed that this box was rather hot.
Now the good thing with the top of this case is that the pastic on top actually does allow some air flow. So I an going to mount either 1 large fan, or 2 smaller fans on the top of the case to get some better air flow.
What I have done to reduce noise is out holes that normally come with the case where the fans are suppose to go.
So instead of having about 90 or so little holes that will whistle away, i have on large hole.
The other problem that every one has with fan blowing in DUST. One thing I have down with all my intake fans is to secure some CHUX SUPERWHIPES or some ohome for my motherboard box on the out take side of the fan.
Okay, i does not look pretty, but it i alot less uglier than a seeing a CPU fan covered in dust.