http://www.evworld.com/view.cfm?section=article&storyid=825

Energy CS's 150 mpg Prius plug-in hybrid. Valence Saphion (tm) lithium-ion batteries were installed in place of the Prius' 1kWh NiMH battery pack, which is located under the rear passenger seat. The car is a proof-of-concept prototype, which will make its official debut at the 21st Electric Vehicle Symposium in Monaco next month. The plug-in hybrid concept lets the car run further on electricity stored from the electric power grid instead of gasoline for the first 50-60 miles, effectively tripling the miles per gallon performance of the car.

With ever improving battery technology plugin hybrids will soon gove way to full plugin electric cars.  With no infernal sombustion or greenhouse gas emissions.  But these plugin hybrids at 150 mpg are exactly right at this moment in time.