I drive a Prius Spirit. The reasons are:
1. I can get 55 mpg even on Welsh mountain roads, while my previous Kia Picanto only gave me 38 mpg with far less speed and power
2. The car tax is very low
3. If I was crazy enough to want to drive through London, I wouldn't have to pay the congestion charge
4. I like the idea I'm driving for free when the electric motor kicks in during town driving at 30 mph or slower
5. I enjoy having the petrol consumption display screen. It has taught me to drive far more economically.
6. I bought a 2005 model last February, and have calculated that with the savings on petrol and car tax, and the estimated trade-in price in four years time, the car will only have cost me fractionally more than the trade-in price I got for my old car.