it will stop growing in the next 2 years,its growth has already started to decline
plus the fact that Social networking work on the basis of COOLNESS and new exciting thing which will hinder Facebook's longterm sustainability
facebook as a service with mail and other networking will exist for long time
but it would be nowhere near where its today after 3-4years time and won't be known as social networking
kinda like google,it will turn into a big corporation







