"Stones of Significance" (a short story by David Brin)
http://www.davidbrin.com/stonesofsignificance1.html
MovieLens Unplugged: Experiences with an Occasionally Connected Recommender System
http://citeseer.nj.nec.com/584995.html
Collaborative Filtering resources
http://www.sims.berkeley.edu/resources/collab
"...frequency and recency are the best predictors of what you'll want next."
http://surfmind.com/musings