Hacking Recommenders
Here's a rather unusual recommendation. If you are interested in this book by Pat Roberston, the TV Evangelist and notorious homophobe you may be interested in this gay sex manual. This recommendation is not only unusual but it created a bit of a stir in the press and was an embarrassment for Amazon
This freakomendation is a result of a small group of folks purposely manipulating the Amazon recommender. These folks merely had to visit Pat Robertson's book and then visit another book. By coordinating their actions and visiting the same book (the gay sex manual), they were able to manipulate Amazon into making the recommendation that would make Pat Roberston blush.
Credit to Bamshad Mobasher for this freakomendation and the screenshot.