[MetroMPG]

basjoos - another consideration is that you drive a lot of miles in a year.

Where a person does a lot of driving, regular back of the gas receipt "instrumentation" can be practical as a way to hone useful techniques, because the feedback is timely enough.

On the other hand, I put gas in my car 5 times last year, 13 times in '06. That lag between cause & effect makes it much harder to learn about a particular car's peculiarities and/or develop new skills.