I've never worried much about it. I buy an efficient car, and then I just drive it. While I lived in Fargo, I had the lowest mpg of anybody on Prius Chat, due to the cold and my very short commute of 3 miles / ten minutes. And the fact that nothing in Fargo was very far from anything else. Lowest mpg, but also (and this is far more important!) lowest total amount of gas burned. Now my Prius only gets used for the longer trips where it really does get good mpg. (Or very occasionally for hauling recyclables to the recycling center.) Otherwise, it's zero gasoline for me.
