Used-book stores are filled with books, dusty, old, sinus-polluting books and, as if that weren't enough, with the kind of people you make a conscious effort to avoid during the day  ne'er do-wells, layabouts, semi-employed dissertation candidates and self-proclaimed bibliophiles who consider writers such as Walter Benjamin, dead since 1940, their real friends.  Used-book stores are not where you absorb relevant knowledge; they are not where you go to bone up on Steven Pinker's latest thoughts on cognitive theory, to peruse the newest campaign biographies or to sneak a cheaper copy of "The Da Vinci Code" so you can affordably keep up with cocktail conversation.  If you like to make the most of your life, used-book stores can seem an absolute waste of time.  That is precisely what makes spending time in them so worthwhile. 