Robert X. Cringely [1]:

What will likely happen to social networking is that some applications will survive on a more modest basis than now (used by the trucker equivalents), others will morph into some new Next Big Thing as their more compelling sub-applications take over, and true hard-core social networkers will jump to more advanced technologies that eliminate the riff-raff. In the meantime, 70 percent or so of most social networking functionality -- the really useful functionality -- will be sucked into the dominant portal/search/e-mail/chat/social networks like MSN and Yahoo.