I have had my Prius C (2 - black) for one week and love it. I am new to hybrids and have been astounded by the initial mileage I'm getting. The car tells me I'm averaging a little over 50mpg after 250 miles of mixed city and highway driving, but manual calculation of 247 miles on 4.2 gallons of gas is 58.8 mpg. Again keep in mind this is my first hybrid. Great car!
I just had my first fillup. I went 460 miles on 8.9 gallons of fuel for ~52mpg. However, the mileage calculated by the prius was 56mpg. The first tank also incorrectly calculated the number of miles left in the tank (off by hundreds). It seems to be coming up with more reasonable numbers on this tank though.