I want to leverage one of these for a project.. I like the idea of Facebook Connect letting you send activities to the person's wall etc, when they do stuff on your site.. it would definitely help spread the word about the site.. but, you're restricting your site to facebook users only. Google Friend Connect is more purely about the authentication, but it uses OpenID, so they can sign in with a variety of different accounts they have.. Gmail/Google, AIM, Yahoo, or a general OpenID address.. widening the net on who you're welcoming to the site. Any opinions? The project is a localized listing of restaurants/delivery-places for my area so users can view menus, rate, and comment, which i'm probably putting together with Drupal.