I just got my finalize button today, so I won't actually have my Model S for a couple of months. One of the things I'll have in place is a circuit meter on the NEMA 14-50 in my garage to measure the actual amount of energy the car is using. This would be power to charge the battery, power to replace "lost" vampire draw, power to heat/cool the pack... basically all the additional electricity I'll have to buy, for whatever reason, resulting from my ownership of a Model S. I'd then like to calculate my actual miles per kWh and electricity cost per mile. (My understanding is that the car's own systems only report on energy drawn from the pack, and doesn't take into account charging inefficiencies, pre heating/cooling and so forth). I'm wondering if anyone has done this and would share results. My guess is that the car actually is responsible for more electricity use than the Tesla advertised 300 Wh/mile (= 3.3 miles/kWh).