I think most Prius owners would agree that having current mpg dispayed as realtime feedback on the MFD causes them to change their driving habits. Personally, I find the feedback fun and useful, and I don't think its just the Prius. I'm certain that if I had this instant mpg feedback in other vehicles I would drive them more fuel efficiently as well, especially given recent high gas prices. I can't help but wonder, how much we, as a nation, would save if all cars were equipped with a mpg display. On a technical note, how easy would it be to retrofit a modern car with such a device? With many cars sold stock with electronic fuel injection, wheel rotation sensors, etc, and the availability of cheap electronics, I bet it could be easy done on many makes and models as an after market add on. No new vehicle, no new infrastructure, no new fuel, just a small shift in driver awareness/paradigm to get us moving in the right direction. The biggest change in global energy policy will start between our ears.