Do you do this? Now that you're using the Netflix Friends feature, do you rate your movies differently, because you're aware your friends will be seeing your ratings? Cory Doctorow describes it in his article on "Metacrap" , how our self-consciousness affects how we rate things. The result is useless data.
I'm guilty. Because I am conscious of the influence I have when I rate a movie, I am very cautious about giving anything a five unless I unreservedly love and recommend it to everyone. I have very few movies I "hate" as well, because I'm conscious that I could be keeping people from watching it. Nearly every movie I rate falls somewhere in the middle between "watchable, but ordinary" and "very good, but not great"