In my search for info on calculating EV efficiency, came across this interesting article with java calculators: http://www.ecoworld.com/transportation/the-battery-powered-car.html
The articles mention that standard EV car efficiency is around 4.4 kilometers (2.7 miles) per kilowatt-hour.
My little scooter gets around 40 watt-hours per kilometer on SLA (I need to get new figures for the 43.2 volt NiMH packs). Flipping that around, that's 25 km per kWh. That's around 16 miles per kWh.
Another interesting article as to why the Chevy Volt isn't using A123 packs: http://www.technologyreview.com/blog/editors/22186/