Aluminum major panels (hoods, roofs, trunks, door skins) have been used in cars for quite a while. In living with them, specifically daughter's 2003 Dodge, even minor body damage often results in remove and replace for repairs. It cuts down on rust worries certainly but doesn't address the easily dented complaints that many of us have for thin metal in spite of what the article states. Rule of thumb is 1% fuel economy per 100 pounds so that the weight savings should be responsible for about 7% FE improvement by itself.