This occurred with almost devastating consequences. I was driving downhill on a twisty highway in the Santa Cruz mountains. I kept smelling burning brake. I just assumed that it was from all of the cars on this road. I hit the brakes and the pedal went to the floor. I was able to bring the car to a stop (thank god) by riding up on the dirt shoulder. When I got out of the car the brake hoses were on fire! I had the car towed back to the mechanic and basically replaced the whole rear braking system. Apparently the problem was with the parking brake cable sticking (the car sat for three years). At first I thought that I was the most stupid person ever having this happen due to not releasing the parking brake. I checked the lever to find that I did indeed release the parking brake lever and and had just assumed the brakes released as well. Scary and expensive. Check your parking brake system. Good luck.