Collaborative Filtering (Score 1)

Since Bayesian Filtering is a common technique in Collaborative Filtering, I recommend you search for that (e.g. CiteSeer http://citeseer.nj.nec.com/cs). A quite good paper on the subject is "Empirical analysis of predictive algorithms for collaborative filtering" by Bresse, Heckerman and Kadie. That paper gave me a lot of insight for my diploma thesis. Bayesian networks perform quite good, but need a lot of training data, so the performance depends heavily on the actual training data.