On the cars that I have had rotors replaced, I usually could feel it at low speeds as the car is almost coming to a stop. If you brake from a slow speed quite slowly you should feel the brakes come on and go off as the warped rotor contacts the pad and then comes off the pad. My 560 is currently like this and I am about to get them replaced. It has 70k miles so I think this is about right.

Matt.