Wal-Mart's Weight Effect - Forbes.com: "Our data suggest that we buy healthier food when our purchasing power increases. There is a small increase in consumption of fruit and vegetables in places where Wal-Mart does a lot of business and a decrease--or smaller increase--in fatty food consumption relative to places where Wal-Mart doesn't do business. That is, people might consume more fatty foods, but consumption of those unhealthy goods increases more slowly than it does for the rest of the population."
This goes against prevailing "wisdom" and this is why doing science the right way is so important. Sure, there are lots of studies that confirm the obvious, and we laugh at the scientists. But when the counter-intuitive happens then you have something really important.