Yahoo Green: Do Americans care about fuel economy as oil spills into the Gulf of Mexico and gasoline hovers around $3 a gallon? You bet they do, though they also have a fair number of misconceptions about how to squeeze a few more miles out of every drop. The Consumer Federation of America’s (CFA) most recent survey says that if we had a 50-mile-per-gallon car fleet today, we’d save more oil than the entire proven reserves in the entire Gulf of Mexico. And people care about that. According …