Quote Originally Posted by o_O View Post
Changing gears in a manual is mechanical, using energy from the driver via the clutch and gearstick. In an automatic, the only place that energy can come from is fuel or battery (which is charged by fuel anyway), not to mention the computing power required to stop the automatic transmission from intrusively shifting gears and also to maximise the fuel economy. That's why autos are inherently less efficient on gas. If a driver's driving a manual such that fuel economy is less than it would be in an auto, then they aren't doing a very good job at driving.
Given that fuel savings from using a manual transmission well are often fairly low (especially these days), I'd say your average user will burn through the fuel savings of a manual by simply not shifting as efficiently as a manual, considering most people aren't a computer, and a lot of people driving manuals aren't very good at it. Honestly, I've known as many people who are good with a stick shift as those who aren't, and the ones who weren't had been driving stick for years.

And besides that, it still depends on how well the person drives more than the transmission anyway. A lot of people just plain don't drive well for conserving gas, and reducing vehicle wear and tear.