I'm pretty sure I've mentioned Gnod before, or perhaps I'm thinking of something similar. At any rate, now it should be easier to dig out of the archives. Gnod is a self-adapting system for mapping books, movies and music on the basis of shared preferences. ("If you liked that, you'll like this" - nearly always a lie, of course.) See specifically: Gnoosic, Gnooks and Gnovies.