It might be less complicated then you'd expect (at least one way of doing it): http://en.wikipedia.org/wiki/Collaborative_filtering http://en.wikipedia.org/wiki

It might be less complicated then you'd expect (at least one way of doing it): http://en.wikipedia.org/wiki/Collaborative_filtering http://en.wikipedia.org/wiki/Collaborative_filtering The core idea is linear regression. Here's Google's service: http://code.google.com/apis/predict/ http://code.google.com/apis/predict/. Here's a commercial API service: http://www.directededge.com/ http://www.directededge.com/.