Social applications are — at their basis — a means for us to communicate. Not just point-to-point communication, as in email or in IM, but increasingly a more general communication from me to the network of others that believe that I matter. This is what blogging affords us, and Flickr streams, and even Twitter.
We are sending all sorts of traffic — different sorts of messages — flowing through the various implicit and explicit social networks that we define ourselves through, and through which we discover meaning, belonging, and insight.
This traffic flow — made more liquid by RSS and instant messaging style real-time messaging — is the primary dynamic that I believe we will see in all future social apps. Yes, we will want to have our traffic cached — for search and analysis purposes — but we will increasingly move toward a flow model: where the various bits that we craft and throw into the ether — blog posts, calendar entries, photos, presence updates, whatever — will be picked up by other apps, either to display them to us, or to make sense of them. We want to consolidate all into one flow — a single time-stamped thread — that all apps can dip into.