Rate GM's XFE - Is it worthwhile?

How much Extra Fuel Economy?

According to a number of sources, "General Motors will produce for the 2009 model year special fuel economy models of four of its biggest, thirstiest trucks, the Chevrolet Silverado and GMC Sierra pickups and the Chevy Tahoe and GMC Yukon SUVs." Ultimately, the new vehicles will improve city and highway fuel economy by 1 mpg. Obviously, when fuel economy is already low, any extra increase in fuel economy is a good thing, but is one mile per gallon really meaningful?