Jonathan Welsh had an interesting article recently in The Wall Street Journal about why - despite myriad technological advancements - your car's gas mileage still sucks. (And it's not the political axis of evil, I promise.)
He makes the point that cars made in the '70s and '80s had better gas mileage - some like the Ford Fiesta up to 50 mpg - than those made today. Despite huge technological advancements in other areas, fuel economy is pretty much unchanged or worse.
Part of the problem, he says, is vehicle safety. People decided heavier vehicles were safer - and even the safety gear added to cars today make them heavier.
Cars also are larger overall, and models that started out as subcompacts have grown to become more like midsize models. Honda Motor Co.'s Civic CRX, a mid-1980s two-seater of 20 years ago, was 12 feet long and weighed about 1,700 pounds. (See photos.) Today's Civic sedan is nearly three feet longer and weighs about 900 pounds more. Even the smaller Honda Fit, considered almost impossibly small today, is larger than the mid-1980s Civic CRX.
He points out that most technology on engine performance concentrates on horsepower, not gas mileage. So cars are faster today - but your gas mileage still sucks. ;)