Ok but it's still a lot. But we have to keep in mind that the most important thing for a social network is the userbase. I think it will be hard to get people off facebook.
You would not want the Facebook user base now anyway, there are greener pastures now. WhatsApp, Snapchat, Instagram, Kik. Although a lot of those already belong to Facebook, so I guess the point is moot.
Sphere has to offer something special to attract a niche audience. Then expand if successful.