Frozen Caliper
After 52,000 miles of trouble free driving, my 2002 Prius had a frozen brake caliper. As Gene Godefroid noted, the car did not pull when braking and it seemed to handle the same. What I noticed was that the mileage dropped from about 43 to 35 mpg, the car would not stay in stealth mode and it seemed to have a bit less power.
I checked the tires to see if the pressure was too low and that is when I noticed that the passenger side disk brake had some deep groves in it while the other disk was smooth.
I remembered Gene's post and decided to do a test. I drove the car for a mile and then checked the temperature of the front brakes. The drivers side disk was cold and the passenger side disk was hot. The next day, I took the car to the Toyota dealer and they confirmed that the caliper was bad and that the disk and pads also had to be replaced. The parts were not available and had to be ordered. It took a week, but I finally got my car back and the mileage is back to normal. Toyota paid for the caliper ($390.00), under the extended warranty, but they would not pay for the disk or pads.