One of the biggest hurdles any social network service faces is getting users to sign up (or in Twitter's case, to come back). Facebook knows this well, and has been seeking for ways to encourage more people to join. Obviously, the less hurdles there are to overcome in joining a service, the more readily people will turn to it. Embracing that ideal, Facebook has recently implemented support for OpenID, a relatively new service that tries to homogenize online profiles. As a result, anyone with an OpenID account will be able to login to Facebook, using the same credentials for multiple web services.
The move is certainly a plus to the popular social network, but it's also a sign of how things have been changing online, with more sites willing to integrate other companies' services. Is this heading towards an Internet where a single portal is responsible for all your online communication? That may be a bit far off, but watching it develop is certainly interesting. OpenID is a direct example of that, a free and easy way to use a single digital identity across the Internet.