What are you doing for viral growth? Like, why should I tell my friends to sign up?

Have you thought about setting up some type of system to automatically create profiles for people? You could scan in the front page of a printed thesis (where it lists the advisers), extract the names, and then add pages if they don't exist for those professors and PHD people. Then, when a PHD student googled themselves, the phdtree link would show up.