In the book Heat Monboit argues the stats show that when someone "greens" their consumption they also increase it. For example switching to "green" energy meant people stopped thinking about conserving.

In the specific case of electric vehicles (and many plug in hybrids) luckily they're such an immense improvement that my guess is that they still have a net benefit. But far from the simple efficiency math, and more likely the user will increase their consumption by some meaningful percent.