Definitely deregister a reader (Sonys and Kindles at least) before giving or selling it to someone. If you don't, they want be able to register it to their account. I sold a Sony reader to someone a year ago and forgot to deauthorize it (Sony's term for deregistering). Unlike the Kindles which can be deregistered regardless of whether the device is connected, you can only deauthorize a Sony reader if it is connected to their server. Since I had already shipped it, I could not connect it. So I had to call CS and spend a long time with those idiots before they managed to deauthorize it. Fortunately I caught my booboo and got it deauthorized before the buyer received it in the mail, so she was able to use it with the Sony Store right away.