I think the growth will be in the use of smaller, more focused, niche social networks that cater to a particular interest, hobby or vocation. These smaller sites will allow like-minded individuals and groups to connect, exchange ideas and receive genuine and useful support.
These kinds of sites will also be attractive to advertisers as they get targeted demographics to spend their online advertising budgets on.
Thanks to sites such as ning, anyone can start a niche social network about anything. There's also a search engine to help find niche social networks that lists thousands of networks for a whole range of subjects, http://findasocialnetwork.com