Completing the Virtuous Cycle between Payment and Social Engagement in Freemium Social Communities

I was there in this talk from Dr. Ravi. The talk was about the different business model that are currently employed by some of the social communities, for example, last.fm, Spotify. He mainly talked about the Freemium model, where users are free to use the service from the website within a certain range. But using beyond these service would charge the user. His team has lead some experiments that would increase the freemium users to payment users.