Amazon (AMZN) has quietly launched a grocery-delivery service called Amazon Fresh in its hometown of Seattle. Michael Arrington wonders if Amazon remembers Webvan, the dotcom flameout that spent too much money on trucks and refrigerated warehouses and went through ungodly gobs of cash in the process. But perhaps it's got its eye on Fresh Direct, which has become a fixture in New York City over the past few years. Online groceries can work if you target dense urban areas and extend service only into those areas where the demand is likely to be the greatest. Like most food businesses, it's more of a hyperlocal play (neighborhood by neighborhood) than a national play. The real question is: How many neighborhoods in America can support such a service?