Heat pipes are most often seen in laptops, where the heat produced by processors and graphics chips can be efficiently moved to more convenient locations for cooling. My Dell laptop uses one for cooling the processor and probably the graphics chip as well. Other places I can think of that use these are the heatsinks in Shuttle's cubelike XPCs and Abit's OTES (Outside Thermal Exhaust System), found on one of their Siluro graphics cards.