From the New York Times:
On Amazon.com, a customer interested in buying the novel “The Life of Pi” is also shown “The Kite Runner” because other Amazon customers – presumably with similar tastes – also purchased that book. That’s just one approach among many in the science of recommendation software.
Web technology capable of compiling vast amounts of customer data now makes it possible for online stores to recommend items tailored to a specific shopper’s interests. Companies are finding that getting those personalized recommendations right – or even close – can mean significantly higher sales.