EPower now is available for overclockers.

http://www.evga.com/products/moreInf...0Hardware&sw=4

Most benefit will be on low-end/middle-end and dual-GPU cards, which always limited on power, or motherboards (for example 775 boards for cedarmill OC)
GTX 590 which I overclocked with only 1.2V using two EPower's was able to hit more than 1000mhz w/o hassle.
On old cards like G92, G71, G80 using UT can get from 50-100 to 200+ MHz, depends on conditions and GPU.

Of course, using this is straight way to kill your mobo/gpu warranty, so only for advanced users. Using is simple, just basic soldering and basic PWM controller function idea is need, no need to have PhD to use these