German sociologist Georg Simmel in the later 19th century. Simmel saw a diffusion effect that in our era of “memes” and “media viruses” doesn’t get talked about very much. There are two mechanisms to Simmel’s effect. In the first, lesser groups seek to imitate elites. This provokes the second mechanism. When elites find themselves imitated, they drop the practice in question and move on to something new.
Google and Groucho Marx – Grant McCracken – Harvard Business Review
So Google+ will rise and then inevitably fall or simply become part of the media ecoscape, which as McLuhan points out, we often can’t see for it’s ubiquity.