From David Pogue, here is the story of iForce, an iPhone app that is a magic trick. The issue is that it has a ton of negative (1 star) ratings on iTunes. Those ratings are accompanied by great reviews! The reason is that magicians and others who like the app do not want to many people to know about it or it will spoil the trick. It is like a negative network externality. This is a common feature of magic tricks which have codes of secrecy built up precisely to prevent dissemination. These are ideas whose value, like insider information, comes from restricted access.