For individuals, the matter is somewhat cut and dry. Which of these sites provides me with some kind of value? Which and how many of these sites do I want to use or are able to use efficiently? Obviously, with the immense growth in this space keeping track of the latter can even be difficult if not impossible, but aggregators like ping.fm and FriendFeed are stepping in to help you wade through the madness. I, for one believe that social networking's usefulness, as well as the usefulness of the internet in general, lies not only in the value provided to users, but the overall aggregation and organization of data from multiple sources into easy to find resources. The internet has grown to an enormous size, and even search engines like Google are finding it more and more difficult to provide you with the information you want (Enter the idea of semantic web technologies, and answer engines).
For businesses, the obvious question is "how can these technologies drive growth and more importantly, revenue?" Unfortunately, answering this is a bit like hitting a moving target. Forecasting and postulating around stable technology environments is often difficult, but doing so in a world where Monday looks nothing like Friday...well, that's daunting at best. The good news: it's easy to recognize that the strength of these systems is the ability to organize enormous amounts of people around ideas, interests, likes, dislikes, where they live, etc. What's more, that ability to organize globally (something that was historically nearly impossible) is free to leverage in a wide variety of ways. For instance, California based Benziger Winery provides their Facebook friends with information on current sales, harvest schedule, and events through status updates. Cisco's CTO publishes updates on her activities and the activities of her company through her Twitter account. The bad news? Falling behind here puts you at an exponentially increasing disadvantage against those who are embracing it. The difference between the winners and losers is not only leveraging a cost efficient way to market and communicate...but the ability to control that message rather than someone controlling it for you.