I was trying to find a real comparison of MIPS of this thing compared to an I7 and landed on this page for performance data for the RPi. The most interesting thing to me is power consumption data at the bottom - that shows idle with network is around 370mA, which should mean (ignore power supply efficiencies) that 64 of these things should use about 120W at idle.
If those are switch-mode power supplies most of the that current will be drawn out of phase (ie. imaginary power); not important to the domestic customer, as the meter probably won't read it, but important to the supplier, who will come and make you fit power correction equipment to your supply :-)
http://www.elinux.org/RPi_Performance