going commercial with socials

This week some article inspired me: The times are gone were social networks are a playground. Rather the time has come to build commercial applications leveraging the social network functionalities. Just Google published an API for the the Google+ http://goo.gl/RHygO

Now I wonder: What might be good business ideas for that? Which service could be set up that is such good that people would pay for that? I don’t mean building a website with some social content and get the money for the banners; rather I mean the content itself.