hmm...well i could be wrong here BUT....
i too sorta expereience the same shit...like if yer going fast and u start to brake the whole brake pedal shakes and shit and it feel like u have no brakes left?
i belive its just the Anti-lock brakes actually...cause the way they are designed to stop the car is to continously "grip and release" so that this way yer wheels dont lock up.
Like sometimes if i just cover the brake pedal with my foot u can feel the anti-lock brakes working.
This is just a guess cause i too thought similar but i was like "shit i only got 2,000 miles on the car theres no way i ruined the brakes already?"
So there's yer answer bro....hopefully it is what im thinking.