Never, ever, ever. I may be able to re-watch a movie, but I have never been able to bring myself to reread a book, re-watch a series, or replay a game. I love endings and I respect them in the sense that once it's done, then it's done. There's something about going back to the beginning after finishing something that feels almost wrong. If an author or television writer shoehorns an extra book (The Mortal Instruments) or season (The Following) after having a clear-cut finale (for the sake of some extra cash), I won't read or watch past what their initial vision for the ending was, either.
It drives my fiance crazy. I've told him about so many anime and television series that I've watched and know he'd like and we'll watch a couple of episodes and then I just let him fend for himself. I can't!