Comment by quotedmycode

From what I understand, they never implemented any of the algorithms, because their existing one was good enough, and the premise has changed. It used to be, you'd make suggestions so people could get DVDs sent to them, and you'd know they would enjoy it. Now with streaming, the cost to send something you don't like is cheap. So the recommendation engine just has to come up with something you'd try to watch and perhaps enjoy. If you start watching something, it's not your taste, you switch streams. So there's not a lot to gain from improving recommendations 10% unless they were pretty low quality ratings to begin with.