Fast cores take exponentially more energy than slow ones. So the solution is to use more slow and simple cores instead. We get more performance per watt that way. On PCs we can use GPU's to make computations in parallel. I guess this is like that, but for servers.

FPGAs are excellent for parallelizing IO, so if the application involves lots of IO, an FPGA coprocessor will likely reduce power consumption if the CPU delegates IO intensive operations to the FPGA.

Tell that to Microsoft.

http://www.eetimes.com/document.asp?doc_id=1324372

Because they can accelerate arbitrary algorithms anywhere from a percentage to 50x increase often for a fraction of the energy and clock rate?

I'd guess more so when sequential part is on top tier CPU and accelerator is on its NOC.