Paperbacks became popular during the War. Cheap and portable, the books benefited from the condition of "hurry up and wait" during wartime which left servicemen and others hungering for a way to while away the time. Lending libraries grew in popularity, too. Meet today's version: the Paperback Swap. The free site allows you to swap books (hardcovers included) with others by registering and listing nine books you'd like to receive from other members and nine books from your library you are willing to mail to other people. The only cost is the postage for sending your book to another reader. Reading was never cheaper.