Driving the Prius to work this morning, I was not paying too much attention to optimizing the mileage, but everything seemed to work out, and on my 20 mile (32 km) drive, I got 63 mpg (3.7 liters per 100 km for those of you in the metric world, i.e., every country but the US!). My previous best was about 58 mpg. This little trip cost me about $1.30 for 0.32 gallons of gas (at $4.09 a gallon).
When I first got the car in June 2007, I was getting around 45 mpg on my benchmark route, but over time it has tended to be 48-52 mpg depending on conditions. It's a mix of suburban streets, secondary roads, highways, and interstates, and on the interstates, I tend to drive around 73 mph which is not ideal for the Prius hybrid system. Today the traffic was flowing a bit slower on the I290 and I495, around 65-69 mph, and with cruise control (and no A/C) this really helped to ration the gas.
I really do like the Prius!