"Eric's Dvds", "Owned", "lord of the ring", "love It. dan", "hell ya!", "box", "seen at the cinema", "2" are just a few of the less interesting gems for Forrest Gump. There is nothing to stop MovieLens from analysing private tags if it anything this has the benefit of greater personalisation while not creating a steaming pile. Sure "owned" has some sort of a correlation toward rating but this has no benefit to the community and is just clutter.