This year, we've learned that nothing is too big to fail. Yes, in dire economic times-and in certain circumstances-even Wal-Marts can go under. But what happens to the giant, empty buildings the company leaves behind?They become churches. Or Spam museums. Or go-cart racetracks. Julia Christensen of MIT Press takes Slate on an awesome visual tour of shut-down and re-purposed Wal-Marts in "Big Box Reuse."(Photo: The Calvary Chapel of Pinellas, Florida, purchased an abandoned Wal-Mart and turned it into a church.)