Forgot to add..

..that if you went with Supermicros new 1U Twin (Houses 2 x Dual Quad Core servers) they draw around 360W at full load.

So, 42 in a rack would draw 15kW and give you 168 CPUs, or 672 cores. So for just 42 CPUs (Actually 44) we'd draw 3.96kW - Nevermind though, it all sounded good about blades in the marketting and spin department I'm sure. :)