I have 10 fans in my case. Whenever I turn it on, it sounds like a 747 engine. lol. Well at least they move a hudge amount of air.
Of course I dont run all the fans on a normal basis. I just use about 2-3 normally. I only turn on all 10 when Im at a LAN, and the room is 90+ deggrees. Those LAN rooms packed full of people and running computers always seem to heat up so fast no matter how many doors we open...lol
Most places that have huge computer labs, such as schools, colleges, government buildings, etc. have air conditioning in each room, so the computers dont bake up the room.