I am not disputing the value and importance that a car's gas mileage plays in car purchasing decisions. If it is important to you, that is all that matters. That said, here are some common scenarios the I see or hear about that leave me scratching my head.

1. People who choose to trade out their paid off vehicle that is perfectly serviceable and in good running condition for a car that gets double the gas mileage, but also comes with a car payment. Again, more power to you if you just really want better fuel economy. Just don't use savings on operation costs as justification.

2. People who get caught up in the number next to MPG to the extent that it becomes the end goal. Crunch the numbers. If you put 15,000 miles on your car every year, and it gets 30 MPG you will pay $1500 for gas, assuming it is $3 per gallon. If you drive a car that gets 15 MPG you will pay $3000. That is significant, but people who are considering cars that are in the 30 MPG category aren't going to consider vehicles in the 15 MPG category. Typically it is more along the lines of a 37 MPG car versus a 32 MPG car, which would yield a difference of $190 annually if you drove 15,000 miles and gas averaged $3 per gallon over that time. For $15 a month I would be happy to drive the car with worse mileage if I liked its other features more.

If MPG is your thing, great. Just be honest about the real pros and cons of your ownership decision. If the annual cashflow of that $300 or $400 would be better spent elsewhere, great. At least make a "big picture" decision and not one focused on one data point. My personal opinion is that I spend 6-10 hours a week in my car, and if I'm going to spend the equivalent of 12 to 20 days in my car each year I want to drive a car that I like. I put much more value in the driving dynamics of a car than I do in its fuel economy. People who have the opposite philosophy are welcome to do so, and that's fine.