The BellKor solution to the Netflix Prize

http://www.netflixprize.com/assets/ProgressPrize2007_KorBell.pdf

Here's the tell all story of how the leaders in the NetFlix Prize did it - A step by step guide to all the 107 steps to glory. Glory in this context is defined as a RMSE score of 0.8712.

I don't begin to understand more than one underlying point of this document. And, that point is that none of their individual optimizations worked near as well as a blending of the methods.

These people don't mind telling you how they do their work. A background document can be found at:

ftp://ftp.computer.org/press/outgoing/proceedings/icdm07/Data/3018a043.pdf