What technology goes in behind the screens of Amazon recommendation technology? I believe that Amazon recommendation is currently the best in the market, but how do they provide us with such relevant recommendations?

Recently, we have been involved with similar recommendation kind of project, but would surely like to know about the in and outs of the Amazon recommendation technology from a technical standpoint.

Any inputs would be highly appreciated.

Update:

This patent explains how personalized recommendations are done but it is not very technical, and so it would be really nice if some insights could be provided.

From the comments of Dave, Affinity Analysis forms the basis for such kind of Recommendation Engines. Also here are some good reads on the Topic

1. Demystifying Market Basket Analysis
2. Market Basket Analysis
3. Affinity Analysis

Suggested Reading:

1. Data Mining: Concepts and Technique