Re: water vs air (common question)
Technically speaking, most computers are cooled with the use of phase change in combination with other methods. Most, or at least more and more, modern CPU heat sinks use heat pipes which use a liquid phase change to transfer heat to a air cooled radiator. So, technically speaking, there aren't nearly as many "air cooled" CPUs out there anymore.
I have to agree that a fully liquid cooled system is a little more work than it's worth, at least for me. If you are pushing the over-clocking envelope then you will probably need a more efficient cooling system such as liquid cooling or phase change. (Phase change as in gutting a freezer and using the parts to cool your CPU.) I've built several quad core systems with, in addition to the CPU and GPU fans, one or two 120mm case fans running at moderate speed with good cooling and quite trouble free service.