I was a little disappointed in my initial gas mileage on my brand new 2007 Prius. For the first several months I had been getting in the low 40s -- not that much better than any reasonably fuel-efficient car. Everyone said I should be patient, because the car needs time to break in, and I should see an improvement once we hit warmer weather.
Sure enough, look at this display. I'm getting over 60MPG on my commute, which is the only number I really care about since that's the vast majority of my driving.
Since purchasing the car, I've filled it with a total of 85 gallons for an average of about 44 MPG. My most recent tank registered about 48 MPG, so the car is clearly getting better MPG as the weather warms, as the engine breaks in, and as I become more used to driving it.