rather than having rotors that have actually warped, its far more common that you have uneven pad deposits on your discs, which is caused by heating the brakes and resting on the brakes when they are new (when stationary and new and hot the pad material will scar a new disc apparently).

check out this web site, its pretty handy. http://www.stoptech.com/whitepapers/warped_rotors_myth.htm

pez