Right now, the way to measure success of these programs is related directly to each individual campaign objective. Does the client want to acquire followers, drive page views, impressions to units on the content page, drive engagement? At this point, it all seems relative. But there are social operating platforms like Unified Social/AddThis & others that are attempting to prove value to clients by assigning $$$ amounts to likes, stumbles, tweets, etc. as earned media, while also harnessing user data to capitalize on for later campaigns or initiatives.