I filled mine yesterday!
We own 2 cars and usualy fill both once a month. We drive a total of 15,000km/year. This include comuting, errands, vacation trips and our 2 sons play hockey. In RE, I plan to drive 5,000km/year with only 1 car.
I just cannot understand how much peoples arround us drive so much. With same comuting, same hobbies etc, most drive like 25-40,000km/year and fill the car AT LEAST once or TWICE a week. Even before turning Mustachians, we use to clowndrive like crazy and "just" did 20,000km/year on average!