I would also recommend Yehuda Koren's (Bellkor leader, if I recall correctly) KDD 09 excellent paper, "Collaborative Filtering with Temporal Dynamics" http://re

I would also recommend Yehuda Koren's (Bellkor leader, if I recall correctly) KDD 09 excellent paper, "Collaborative Filtering with Temporal Dynamics" http://research.yahoo.com/pub/2824 http://research.yahoo.com/pub/2824 which speaks exclusively of how to handle temporal dynamics.