I haven't talked about my 2002 Prius for a while, so here's an update.
I now have 132,000 miles on it and have averaged slightly over 50 mpg since purchase. ("That can't be," you scoff... but it's true. I use very conservative driving techniques.) Anyway, if I assume that the average price per gallon (here in California) has been $3/gallon over the past 7 years, then I've spent a total of $7,920 for gas. If I had been using a car getting 20 mpg, the gas cost over the same # of miles would be $19,500. The difference (i.e. the amount of moola saved) is $11,580! That is approximately half the purchase price of the car.
The Prius still drives like a charm, and I've still only had to do routine maintenance on it (oil, tires, tune-ups, filters, car washes). Never, ever had the slightest problem with the engine, transmission, electric... nothing. In fact the brake pads are still original, due partly to the regenerative braking system (which also saves gas).
I hope to keep my car until at least 2012 when Toyota plans to release a plug-in hybrid.