These tools are also called personalized recommendation systems, collaborative filtering or preference elicitation programs and they are usually part of cross merchandising, suggestive selling, and personalized marketing strategies. See also

http://en.wikipedia.org/wiki/Recommender_systems

One of the best known systems is part of Amazon. Very often I find them quite useful. Do you?

Is their usefulness limited to certain products such as books, computer games, videos and music albums? Or can they be applied to virtually every product from food to furniture and consumer electronics equipment? What about websites?

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Topics: suggestive selling, recommender systems, personalized recommendation syst, collaborative filtering, preference elicitation, cross merchandising, upselling, personalized marketing