AFAIK the factor is more like 50x now (Tesla's panasonic packs vs. gasoline) [1]. The thing is, in order to have a fair comparison in energy density, you should compare with the weight of the whole drivetrain, which lowers the advantage of gasoline quite a bit (due to a heavy motor and transmission) [2]. You also have to consider the significantly lower energy conversion efficiency of ICEs (3-4x). All in all I'd expect the difference is more like 2x, otherwise it would be impossible to have EV cars with a more than two thirds of the range than ICE cars of similar size, weight and power (Tesla S vs. BMW M5).

Edit: IMO the main disadvantage of EVs today is not the energy density, with that they're almost on par with ICE. Instead it is the rate at which energy can be refueled. Driving a Tesla for long distances is still a hassle. That's why I see EVs mainly as daily commuters in the near future, while for weekend trips people may just rent an ICU car.

[1] http://boards.straightdope.com/sdmb/archive/index.php/t-7709...

[2] http://www.greencarreports.com/news/1104121_electric-car-ene...

And yet combustion vehicles don't have 2000 miles range. Energy density is very important, but you can make up for it with better efficiency.

But the beauty of adopting electric cars now is that when a better battery technology is developed it can be replaced in cars on an individual basis, whereas a reason we don't drive hydrogen cars today is because fuelling stations would need to stock that in addition to traditional fuels. Supposing nanowire batteries come out for cars: they can still use the same EV chargers.