YouTube takes the business of tailoring your search results very seriously. So seriously, in fact, that it has over 1 million lines of code in place to pair up the videos on its servers to you and your preferences.
This video interview with Christos Goodrow from YouTube talks around—without describing in precise detail—YouTube's search algorithms. He explains why videos are no longer ranked by view count—and gives away just a little bit of detail about what they're using instead. [Computerphile]