when you drive @ higway speeds and come to exit off highway and slow down with brakes if your steering wheels shimmies then your front rotors are warped. if you are at a slow speed and almost coming to dead stop and feel a pulsation in the brake pedal that also is indication that your rotors are warpped. only the front though no need to worry about the back unless your taking corners and pulling the e-brake.
cost your about 150 at a dealer ship to do it. or take them off yourself and take them to local autostore that turns rotors for about 15 a peice.