B. O’Donovan. (2005)introduces the notion of trust in collaborative filtering.
A simple memory based method is used to incorporate trust into a simple similarity based collaborative filtering algorithm. Results on MovieLens seem to be better than standard methods..
F. Carmagnola, A. Loffredo, and G. Berardi. HT '09: Proceedings of the Twentieth ACM Conference on Hypertext and Hypermedia, New York, NY, USA, ACM, (July 2009)