When folks discuss whether the car "knows" it needs brakes or not, they forget a couple of things about how condition-based service works. I've owned BMWs for along time, including an E28, which had the first iteration of the SII (service interval indicator). Same basic idea--the car calculates based on a number of variables when it needs service. BMW has always insisted that when it comes to fluids, it knows.
CBS as an evolution was basically an acknowledgement that fluids need replacing at different times--not at the time of an Inspection I or II under the old system--all it was doing was varying the time you had left until it triggered a warning. CBS parcels this stuff out by mileage and time.
My point? It's this: BMW has good data, I think, on fluid replacement intervals based on their knowledge of the internals of the engine and the fluids in use at time of manufacture. They're not so good with brakes. I don't know how CBS calculates brake time, but it seems to do it on a straight mileage counter--something that doesn't take into account how hard or soft you brake, how often you brake, etc. CBS is fine for everything except brakes. So don't trust CBS to tell you when you're out of pads.
What will tell you when you're absolutely out of pad is the brake wear sensor, which will get destroyed if you're that low, which triggers the BRAKE light. CBS may or may not agree with this, but if the wear sensor has snapped, you definitely need to look at the brakes. CBS might say you have a bunch of miles left, but the wear sensor doesn't lie unless it was damaged or dislodged by something.
BMW dealers will not re-use rotors. With reference to the OP's service, the price is reasonable--for a dealer (I wouldn't use a dealer either for brakes out of warranty). You could probably have gotten an indy shop to do all four wheels pad and rotor for $800 or so. But this doesn't sound like a nosebleed--just dealer prices.
But brakes in general with BMWs? Don't trust CBS--take a look at your pads periodically. That would be my $.02.
BTW, I sympathize with the OP--out of town, wife has the car in service, it's hard to say no, especially when it means another trip and dropping the car off somewhere else. "Unsafe to drive" seems unlikely unless she was driving around with her foot on the brake all the time and there sparks flying off the wheels from caliper hitting rotor. They tend to be pretty conservative in these matters. Not that I'm saying you should drive your car to that point, but I doubt it was unsafe to drive. If I had done it, I would have asked for the parts back--I think that's just a way of keeping a dealer honest. Once I've seen them, they can have them and recycle them. But I want to see them.
Last edited by dmorga1; 10-07-2011 at 10:58 PM.