Brand new to this site (Howdy, Howdy). In reading about plug-in hybrids, I haven't seen anything to indicate that the experimenters use their house-current connection to do any more than charge batteries. But another big improvement would be to add an engine cooling-system heater, or a headbolt heater, to keep the engine semi-warm all night. Any I.C. engine kept warm in this way will start easier and reach operating temperature faster, with significantly less engine wear, fuel consumption, and polluting emissions. Plug-in heaters are very common on big trucks, and have been widely used on ordinary cars in cold northern regions for decades. But they provide the described benefits even in temperate climates. I think they should be included on all new cars, especially since they are simple and cheap. But in the meantime, anyone can add such a device to his/her own vehicle. All my cars are plug-ins.