I really liked Greg's commentary on RMSE -- summed up my thoughts better than I could: http://glinden.blogspot.com/2009/03/what-is-good-recommendation-algorith

I really liked Greg's commentary on RMSE -- summed up my thoughts better than I could: http://glinden.blogspot.com/2009/03/what-is-good-recommendation-algorithm.html http://glinden.blogspot.com/2009/03/what-is-good-recommendat...