While most people simply associate authentication services with a unified method of managing their sign-in activity across several websites, Facebook Connect does much more than simply letting users log in to a site by validating their identity via their Facebook account. When logging in with Facebook Connect, users bring their Facebook profile data with them. This means the website or blog they just logged into can allow them to find their friends who also use the same site. Furthermore, they can share information and experiences using the same features as they would on a Facebook application. With Facebook Connect, almost every feature that you can build with an application on Facebook can be offered through a third-party website or application using the service. - giovanni gallucci