Grouped is a well-written, concise, and relevant summary of the latest thinking in social networking and social influence. It's like the crib notes to a four-year degree in social psychology and sociology. Beautifully laid out and designed to be easily consumable, it quickly covers the fundamental ideas and research about how and why we connect with one another, how ideas spread, how we make decisions, and why this all means that "permission marketing" through social networks is likely to be more relevant and effective than current "interruption marketing" of mass media advertizing.
It does read at times like an advertisment for Facebook (indeed, a cynic might pigeonhole this entire book as a "white paper" for Facebook Ads), but I know Adams better than that (having had the pleasure of working with him at Google on the early stages of Google+), and my take is that Adams sees Facebook as out in front of an important shift in the way advertising will work in general (perhaps this is why he now works there), so Facebook merely provides the best (and in many cases only) example of putting his ideas to work in the real world.
Beyond the explicit goals of developing better marketing campaigns, Adams makes the case (and I firmly agree) that the content of this book is essentially required knowledge for all of us as we move into an increasingly interconnected world in which our social networks (real and digital) and our "predictably irrational" brain help us navigate the endless, swelling seas of information surrounding us. Despite working in this field for years, I learned some new things and found myself nodding in approval at much of the rest. So if you're new to these ideas--or even if you just want an efficient and enjoyable refresher course--this book is well worth your time.