The unveiling of the new Prius, and its half-mile range EV-mode, brought this topic to the front of my mind. More electric range means carrying around more batteries, which isn't always greener:
Green Car Congress: Study: Meaningful GHG Benefit from PHEVs Requires Low-Carbon Electricity
I attended a lecture given by one of the authors of that paper. The additional weight of the batteries drives up the car's energy consumption, and the environmental impact of manufacturing the batteries is also a consideration. Worse, the CO2 emission from (American) electric generation means that you're hardly reducing your carbon footprint by plugging in your PHEV.
I think we should pursue all research avenues, but it's clear we should focus on reducing the carbon intensity of our electric generation (in America, at least) before we spend a lot of money on plug-in and electric cars.
Once the electric car becomes a commercial reality (within ten years), the electric SUV will follow. If we respond by installing more coal-fired power plants, then we've taken a big step backward.
Abolish gasoline taxes. Replace them with carbon taxes. Only then will the market make an educated decision about which technologies are the best choice.