When I was in college, at the end of each semester we’d go to the book store (you know, that place that fleeced us with $100 used books) and we’d sell back those books for about one tenth to one quarter what we bought them from. We’d then use that money to help fund one of our books for the next semester (or beer). Well, Amazon is doing something similar now. Although it has to do more with when new editions of the book are released. Each edition of a book allows you to trade the book in for new editions. Take Practical C++ Programming, from O’Reilly. Apparently I bought the chipmunk book at some point. In fact, considering the fact I can see it on my shelf from where I’m sitting I am certain of it (unless I am hallucinatin’ again – in which case I would really hope for something better than a freakin’ tech book). When I go to the page for that book on Amazon, they know I bought it (they sold it to me after all) and they’re kind enough to offer to buy it off me for about a buck and a half (about 1 / 20th what I bought it for) and sell me the new edition for about $25.30 (or $6.53 used). I know I’m poking at this just a little bit, but that’s just because it makes me think of college. I honestly think it’s a really great feature. There are so many options for things like books and this is just another that will keep me going back to Amazon!