Intel's Xeon Phi cards pack 240 x86 CPUs per card at very low power per core. You can run Linux on them. Soon we'll be serving web content and VMs on them.
The best bang-per-watt supercomputer in the world right now is a ton of Xeon hosts with 2 of these cards per machine.
We've got a stack of then in the office; they're pretty interesting.
One important observation is that the interconnect out of the Phi cards is note very good. While the interconnect inside Phi is pretty good the bandwidth to communicate with other computing facilities is through the PCIe bus. This places the Phi cards close to GPU's very good at graphics and a few specialized problems like protein folding but not supercomputers that can tackle hard problems like sparse matrix solving.
The best bang-per-watt supercomputer in the world right now is a ton of Xeon hosts with 2 of these cards per machine.
We've got a stack of then in the office; they're pretty interesting.