Understanding Referrer Systems
Rashmi Sinha's Recommender Systems overview on Sig-IA is a great overview of the tools used to bring information closer to those that may have an interest in that information. Essentially this gets to the heart of the Model of Attraction. Recommender Systems can provide tools that group information through links that are based on others similar interests. Finding information is what many spend much time doing. Lessening this time and providing methods to predict interests are helpful. This of course takes patterns. Patterns need a breadth of data to be useable.
In particular you may be interested in Rashmi Sinha's "Interaction Design for Recommender Systems". [hat tip Matt]