I can't tell from the README - is your data fairly wide? I'm playing with using Postgres's new K-Nearest-Neighbor support to calculate similarity on 20D cubes, but I suspect my approach won't work well for an arbitrary number of columns (i.e. users x products) unless you first do some sort of PCA or SVD to narrow it down, and it isn't optimized for binary ratings at all. I started writing it up here: http://parapoetica.wordpress.com/2012/02/15/feature-space-si...