Do you have multiple copies of any of your books?
If so, why? Absent-mindedness? You love them that much? First Editions for the shelf, but paperbacks to read?
If not, why not? Not enough space? Not enough money? Too sensible to do something so foolish?
When visiting The Book Thing, I sometimes pick up nicer copies of books I already own. What can I do when they're free!! Recently, I nabbed a hardback copy of Gabriel Garcia Marquez's Love in the Time of Cholera and a nicer copy of Animal Dreams by Barbara Kingsolver. I rarely do this, because I also like to hold onto my original books. And of course, now I've found I'm having a hard time giving up my paperback copy of Marquez' book, since I also like to collect paperback Penguin editions.