Used games, the bane of publishers and the bread and butter of retailer GameStop, is a $1.3 billion business in the U.S. alone, reports research firm OTX. Their findings from the MI6 summit breaks down the used games biz, showing the buying habits of folks who dabble in the pre-owned, all of which is detailed at the report at Gamasutra.
http://kotaku.com/378056/49-million-us-gamers-buy-used-games-to-the-tune-of-13-billion