Motherboards and other associated computer chips can do some amazing things, at amazing speeds.  One of the largest issues keeping computer chips functioning properly at such speeds is keeping them cool.  Processing takes a lot of electricity, and generates a lot of heat.  So why not take that heat, and use it to power the cooling fan for the motherboard?  Why waste MORE power to keep the chip cool, while you’ve got all this extra heat hanging around that you’re trying to get rid of?

Read more about it here :
http://www.engadget.com/2008/02/29/msi-ecolution-motherboard-transforms-chip-heat-into-fan-power/