Three years ago - see http://www.felixsalmon.com/000763.html
Oh welp. History repeats itself.
Each year that the competition was running NetFlix awarded a progress prize to the best ranked team at the end of the year. Part of the requirements of winning this prize is publication of scientific papers describing key elements of their algorithms. BellKor's Yehuda Koren presented a paper at SIGKIDD in July describing the improvements they made to their algorithm to take advantage of predictable temporal dynamics of ratings. Check out the paper here
From an article about the paper:
While movies themselves stay the same, the humans who rate them are anything but static. As Koren puts it, "The way I rate movies today can be very different from how I rate them even tomorrow." To the frustration of Netflix Prize contenders, a four-star rating can mean "great" or merely "so-so" depending on the user's current mood or comparisons with other recently seen movies. Besides such erratic shifts in the rating scale, people's actual tastes tend to change over time -- as when someone tires of action films, for example, and develops a yen for screwball comedies. There's an overall rise in ratings over the years, as well: for various reasons, a typical movie's ratings become more favorable as the DVD ages.
In the past couple of days, a rumor has begun spreading that claims we have changed our policies for third-party advertisers and the use of your photos. These rumors are false, and we have made no such change in our advertising policies. If you see a Wall post or receive a message with the following language or something similar, it is this false rumor:
FACEBOOK has agreed to let third party advertisers use your posted pictures WITHOUT your permission.
The advertisements that started these rumors were not from Facebook but placed within applications by third parties. Those ads violated our policies by misusing profile photos, and we already required the removal of those deceptive ads from third-party applications before this rumor began spreading. We are as concerned as many of you are about any potential threat to your experience on Facebook and the protection of your privacy. That's why we prohibit ads on Facebook Platform that cause a bad user experience, are misleading, or otherwise violate our policies. Along with removing ads, we've recently prohibited two entire advertising networks from providing services to applications on Facebook Platform because they were not compliant with our policies and failed to correct their practices.