one issue with charging an electric car at home is that it throws off the data I get from the electric company that compares my usage to "efficient neighbors" and "all neighbors". since most people aren't charging electric cars at home, it's sort of like comparing apples and oranges. we're generally in between the two data points and it's hard to tell if we'd be in the efficient group if we were able to separate out all energy spent charging the car. I suspect that we're more efficient overall because the increased electricity usage is replacing gasoline, but I don't really know.