Have you worked up your cost per mile for electricity/fuel? I'm curious about how the total operating costs of a plug-in compares to a gasoline car.
These days in my area, probably not that much saved in terms of cost of electricity vs gas, although there is a moderate savings in CO2 production (because in Ontario, Canada, the electricity is cleaner than in most of the US). If I paid all the electricity myself at the lowest rates, I'd probably save maybe a few hundred bucks a year, compared to the current prices of 85-90 cents / L.
OTOH, in my particular case, I still save a moderate amount because I charge up for free at work. I'd say about 1/4 to 1/3 of my "fuelling" costs are paid for by my workplace, because I charge up there, meaning they're paying for the equivalent about a couple hundred bucks worth of gas per year for me.
P.S. I didn't buy this car to save the world, or really even to save more on gas. I did want to buy a used Prius, but the only one I liked with a higher end option package that I wanted happened to be a Plug-in. All the other ones were either base/near-base models, were too old, or had too much mileage. So I spent a few thousand more and bought the used Plug-in. I paid CAD$29000 last year for the Plug-in with 29000 km. With current conversions, that's about US$21500 with 18000 miles.