Bitbender have posted a guide on how to wire up your fans for easy on/off switching control. I might have to take a closer look at this article, quite interesting indeed.
"Have you ever wished you had a means of controlling which fans in your case were on or off without having to fumble about inside your case and mess around pulling and connecting plugs? Here's a very easy mod where we'll show you how to make each fan switchable from the front of your case."More information at Bitbender