I just bought a Ford C-Max Energi; but I bought it strictly for the green carpool-lane sticker.
In California, if you live in a big house, your marginal cost of electricity is shockingly high. For me, it's $0.33/kilowatt-hour.
My Energi goes 20 miles with a 8 kWh charge. That's $2.64 On gas, it gets about 35 mpg. If gas is $3.50 (current price) that's $2.20.
Now, during mid-day on a sunny day, I can charge it much cheaper on our solar panels (currently we are selling power back to PG&E, but at $0.11/kWh) and I do that. I also charge it at work, where it's 'free'; but I live 50 miles from work so I can't keep the car charged just at work. The 'free' power at work won't last forever, either.
You may ask "why not get a Tesla?" Good question. It turns out that there are (at my company) 3x the number of electric-ish cars as there are charging stations, so we have to swap them out after just a few hours. The Tesla would take all day to charge. Also, the Tesla is such a lumbering overpowered beast that it gets substantially less miles-per-kilowatt-hour.