I actually told my bookstore that students this fall could use either the 2nd or 3rd edition of a book (Sipser, which for the record is breathtakingly expensive

I actually told my bookstore that students this fall could use either the 2nd or 3rd edition of a book (Sipser, which for the record is breathtakingly expensive, but the 3rd edition is nearly identical to the 2nd, right down to the typesetting), not really expecting them to follow through. To my surprise, they did---the bookstore website lists both editions and says either is acceptable. ...but if you buy or rent them at the college bookstore, they cost about the same. D'oh. On the open market, used copies of the 2nd edition go for less than a third the price of used copies of the 3rd. (So I sent my students an email apprising them of the situation and suggesting they get their orders in before the thousands of other CS students buying their fall textbooks. :)