Ars Technica recently published an article that the frequent trade-in-ers among us should probably read. In short, if you're not erasing your consoles' hard drives before trading them in, there's a pretty good chance you could be robbed blind. (Or at least robbed astigmatic.)
Seriously, if you're thinking about trading in or pawning one of your gaming consoles sometime soon, follow the helpful tips provided in the Ars piece. They'll ensure that you don't accidentally leave your credit card information in the system's memory for its next owner to exploit. You also don't want to leave your Avatar, Mii or PlayStation Home account on there, either. That's how e-stalkers get started, donchaknow.