Check out this thread:
It is complete with pics and his were worn like that after only 15k miles!
Is your vibration only under braking or when you are driving too? Can you see dark spots on the rotors? Have your tires been recently balanced?
Rotors are fine. My vibration is only under braking, slight but noticeable.
I originally thought it was brakes / rotors as I had a similar issue with one
of my 3 series models. The dealer inspected the rotors and pads and said
they were fine. Their head mechanic drove it and said it was bushings.
It took 3 trips to the dealer and a discussion with the factory rep before
they would fix it.
Tires are brand new. I had the car aligned before installing them. They
have been on now for about 10K miles and look like new. Rotors are
fine and I've just received a new set of pads from Dave Z which I plan
on installing before the snow flies.
I suspect that my dealer ( Gault BMW in Binghamton ) may have only
replaced the single defective bushing. At any rate, vibration is only
slightly noticeable at this point. I'm gong to take a look at the bushings
this weekend to see what I can find.
One thing that will definitely cause bad vibration under braking is to
wash your car and not drive it afterward to get any water off the rotors.
I once washed the car before a trip and parked it in the garage. When
I returned I had very bad vibration under braking. The rotors rusted a
bit under the pads and you could see a very distinct mark on the rotors
where the one section was discolored. While alarming, this disappeared
after about 100 miles of driving.