General Discussion

A plug-in hybrid is a very different beast than an ordinary hybrid. An ordinary hybrid totally depends on gasoline (or, I suppose, maybe there are some diesel models?), with the electric components simply improving gas mileage.

A PHEV can run completely on electric power for a limited range. My Chevy Volt can go for around 50 miles (although that range diminishes to about 35 in cold weather). Since nearly all of my daily driving remains within that range, I'm basically functioning as if I have a purely electric vehicle about 95% of the time.

Once the electric range is depleted the car functions like an ordinary hybrid car, getting mid-40s MPG. It's a great option since there's no "range anxiety". Unfortunately Chevy discontinued the Volt the same year I bought one. There are other PHEVs still on the market, but few (Maybe none? Haven't researched this in a while.) have as much electric range.

The main drawback to PHEVs is the expense of building them, since they have all of the components of both a gas-powered vehicle and an electric vehicle, albeit with some savings from smaller battery size.