Recommender systems form a specific type of information filtering (IF) technique that attempts to present information items (movies, music, books, news, images, web pages) that are likely of interest to the user. Typically, a recommender system compares the user's profile to some reference characteristics, and seeks to predict the 'rating' that a user would give to an item they had not yet considered. These characteristics may be from the information item (the content-based approach) or the user's social environment (the collaborative filtering approach). Some of these recommendation engines are driven by signature patterns (or "DNA") in social behavior (Last.fm) while some are driven by the signature patterns in media genres (Pandora.com).

Date
Media
Problem
Strategy
Interestingness
References
November 21st, 2008
Netflix: Video Rental
Increase accuracy of Cinematch prediction by 10%
Netflix CEO, Reed Hastings, announced the Cinematch recommendation engine improvement competition in October 2006, and no one has won yet, though 30,000 hackers worldwide are hard at work on the problem. Each day, teams submit their updated solutions to the Netflix Prize Web page, and Netflix instantly calculates how much better than Cinematch they are through a live leaderboard.
The “NAPOLEON DYNAMITE” problem

“Napoleon Dynamite,” an indie comedy from 2004 that achieved cult status and went on to become extremely popular on Netflix. It is maddeningly hard to determine how much people will like it. When Bertoni, a 51-year-old “semiretired” computer scientist, runs his algorithms on regular hits like “Lethal Weapon” or “Miss Congeniality” and tries to predict how any given Netflix user will rate them, he’s usually within eight-tenths of a star. But with films like “Napoleon Dynamite,” he’s off by an average of 1.2 stars.

The reason, Bertoni says, is that “Napoleon Dynamite” is very weird and very polarizing. It contains a lot of arch, ironic humor, including a famously kooky dance performed by the titular teenage character to help his hapless friend win a student-council election. It’s the type of quirky entertainment that tends to be either loved or despised. The movie has been rated more than two million times in the Netflix database, and the ratings are disproportionately one or five stars.

Mathematically speaking, “Napoleon Dynamite” is a very significant problem for the Netflix Prize. Amazingly, Bertoni has deduced that this single movie is causing 15 percent of his remaining error rate
New York Times: "If You Liked This, Sure to Love That" by Clive Thompson

http://www.nytimes.com/2008/11/23/magazine/23Netflix-t.html?pagewanted=all