The Prius has definitely been a very geeky car to play around with and figure out. It's been fun to see how various environments and driving styles impact it.
My initial driving in the summer of last year yielded about 42.9 MPG. This was in stop-and-go traffic, but often stopped long enough that the engine would have to kick in to power the A/C while idle. I was able to optimize to about 45 MPG with 72ºF+ auto A/C and on a route that allowed for more constant movement.
The first road trip (1 adult, 2 kids) down I-65 to Florida in the summer yielded tanks MPG of 39-42 MPG. Another road trip to South Carolina with two adults and two kids yielded 39.6 MPG for the trip.
The brutal winter earlier this year was pretty frustrating on gas mileage. The only driving done in the car was done with the engine running constantly just to try and warm up, and I discovered that there's no good way to get a Prius warm enough to melt the ice on your windshield unless you edge it into the sunlight. There were a few tanks that I got 33 MPG on.
We eventually installed Thule Aeroblades on our car which allowed mounting of a Thule Cargo Box. The car got under 40 MPG with the cargo box mounted, but did about 35.8 MPG on the highway drive down. The best tank MPG that I got on our Camry on 100% interstate was still under 35 MPG.
Of course, the biggest gas mileage benefit of the Prius was when we were driving 4-8 miles back and forth on St. George Island at 25-35 MPH. I'd occasionally make trips without the engine even turning on, and the average trip MPG was over 50 MPG.
Almost a year in, this car has been fun to play around with and a great road trip car (especially with the roof rack). The biggest surprise is how it has fascinated my geek side.