“I’ve been experimenting this year with a new book-sharing network called BookCrossing. … The idea, conceived by Ron and Kaori Hornbaker in 2001, is seductive: You sign up for free on their (annoyingly busy) Web site and register as many books as you’d like. Each book is assigned a unique 10-digit ID. Then you leave your books around … and track their travels from reader to reader across the globe.” Unless, of course, no one reports their whereabouts.