Some people will use
DVD Shrink with good results. I have backed-up a couple of my movies with this program by making an iso image of the compressed movie and then just burn the image with Nero. Really came in handy because my copy of Pirates of the Carribean got a crack in it, but luckily I backed-up my copy before this happened. It's simple to use, easy to learn, and gives you some flexibilty in what you are looking to do (keep extras, just back-up movie, etc.).
Eddie