Comment by mhb

You can start reading here: https://en.wikipedia.org/wiki/Netflix_Prize

Netflix used to have a great recommendation engine based on what you liked/disliked. It included all of their members ratings. They had a contest in which they offered $1M to anyone who could improve their algorithm by 10%. The winning team used some kind of customized version of Singular Value Decomposition. The algorithm is public.

I think it is essential to use the negative ratings.