Engadget's article has more info:
Not content with just making its servers bulletproof, HP also wanted to pack more of them into a given space than anyone else on the market, but to do that, the company had to find a way to dissipate the massive amounts of heat generated by super-dense server clusters.
HP found a rather unusual solution to the problem courtesy of one of its executive's pursuits outside of work: VP Rob Noblett's model jet airplane hobby. With the help of engineer Wade Vinson, Noblett realized that the electric-ducted fans he and fellow hobbyists had been using to achieve high speeds more safely could probably be modified to provide the air movement HP was seeking to cool the high-powered servers on its drawing board. After re-engineering the fans to optimize them for cooling instead of thrust, engineers were able build a model called the Active Cool Fan that is both smaller and more energy efficient than traditional fans, even though it's said to force out air as fast as a leaf blower.
I'm not sure how this would be applicable to the home market, blade servers are inherently more secured in place than a laptop, say, or a desktop in the mini form factor. ;)
Model jet plane tech will help cool HP servers - Engadget
update: Some details about the cooling fan from ZDNet.com | HP's super cool computer fans, for instance:
1. At the highest speed, the fan reaches 166 miles per hour (Is this to scale, or real life, I wonder ;) ).
2. The Active Cool Fan design consumes one-third less power and is about half as quiet as traditional server fans. Very neat stuff.