My Alfa will vibrate so badly it'll rattle your teeth if you brake hard from highway speeds. It's done this from the day I've bought it, and three tries at various mechanics to fix it haven't worked, or rather haven't worked for long. According to this extremely interesting article, what my car is suffering from is not warp at all, rather a "cemetite" transformation causing uneven brake pad deposits.

The cure? New rotors and new pads. I was already planning on this, so it's no suprise. However, it's got very good recommendations on how to "bed in" your brakes so this sort of thing doesn't happen again. Highly recommended if you or someone you know is a gearhead.