Hi, we are using Facebook at the moment because icare is in a demo state and Facebook provides personal information that is important for a ride sharing project. Unfortunately twitter doesn't provide us e-mail address and people do not use their real name: we think we need our own authentication system to allow pepole linking their own twitter account. Google+ is an option we are considering. It's not just a matter of API because we are caching facebook likes and friends with their ids to highlight common interests.