It very much depends on the type of driving you do. I have 122k miles on my 535i X and am still running the orginal brakes. My car spends most of its time on the highway and very little stop and go traffic city type driving. To be clear - I am still on the orginal pads and rotors. I am sure there is a BMW spec for required replacement rotor wear due to excessive thinness. If the rotors are warped they should probably be replaced as the shaking and variable pressurers can cause excessive wear to suspension components.