also the sept !05 issue of STARTUNED magazine has an article on brakes and warpage, do a google search for STARTUNED, it's a daimler chrysler publication for independent mechanics.

It mentions the localized area of pad on rotor at a stop after hard usage, and the cooling rate differences between that and the remaining surface of the rotor not contacted.

There is also a recommendation for racing drivers ( cannot remember if this is in the startuned article ) that after any track time slow down but don't keep the pads in contact with the rotor for extended periods or when the car is stationary and cooling down.