You would be making a big mistake allowing your users to log with their facebook credentials. The problem when you do this is you're giving away business to facebook! Am I the only one who is competing against facebook? Wake up and see what facebook does to it's once biggest advertisers like groupon. Wonderful idea, so if they can't buy you out, they become your competitor! They are like the oil men of the early 1900, telephone companies of the 1950's, Airline of the 1970's, etc., Who ever see more is reading this comment, there is a new market out there for social networking sites that will slowly erode at facebooks users, etc., They are called boutique sites, social networking sites that cater to housewives, cooks, etc.,