Proper cooling of your hardware is very important. In most systems cooling is done through a fan on the CPU and some in the case, some people however prefer to use liquid cooling. Today I saw two nice videos on Tom's hardware where they discuss different cooling fluids. The fun thing, beer seems to do quite well as a cooling liquid :-).
Probably not the type of cooling you would use in your data center, but funny enough to watch these videos: Part 1 and Part 2