In the past 12 months, we’ve seen at least three major acquisitions of social networks by larger social networks. Facebook acquires Instagram. Google acquires Waze. Yahoo acquires Tumblr. And we are likely to see quite a few more given the dramatic growth of mobile messaging clients and social networks of all different kinds. While each of these acquisitions has their own particular motivations, underpinning all three is user engagement. Engagement means activity which translates to advertising dollars.