How is the cabin heated? In gasoline engines heat is a by product.
My heating bill is big and I just got a new furnace recently, its been cold here.
There is a built in heater and it does indeed take some juice to run it. Many EV drivers use a smartphone app to remotely start their car 5 or 10 minutes before they get in so that the car is pre-heated (or pre-air-conditioned in the summer) by the time they get in. This works especially well in the mornings since your car would still be plugged in and won't lose charge as a result.
It seems that in worst case situations, while driving in sub-freezing weather with the heater blasting, you can get up to 40% less than the EPA rated range. However, with a 200+ mile car like the Model S, the vast majority of people would still have double what they need in order to do their day-to-day driving.