Among the shops and tourists buzzing about Carnaby Street is a quite respite just off Kingly Court: a book swap shop! Shelves are filled with classics new and old, while inviting velvet armchairs say, "Come, sit for a while." The idea is simple: Bring a book you've read and take one you haven't. There's not even anyone working there. It's all done on the honor system. What's more, there's a sign-in/out book encouraging people to leave their feedback on the book they're dropping off. With millions of excess books in the world, this "leave one, take one" mentality is the best way to pay -- or rather read -- it forward.