Regarding MPG and Paul Barnfather vs Paul
The white paper ( http://www.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf )on the batteries of the Tesla states they contain up to 53kWh of energy or the equivalence of 8 litres (2.11 gallons) of gasoline. If you then factor in the action radius of ~220 miles you get the stated 100 MPG. Considering the cost you get 220 miles for 53kWh*2.7c/kWh = 1.43$ quoting Paul Barnfathers number.
That's 220 miles for the cost of half a gallon (? don't know the price of gas in the states) which will be 440 MPG costwise which is what MPG is an indicator for in any case. This is truly an amazing car!