In his blog post Honestly, do any of us get social media?, Tris Hussey wrote "We’re making it all up as we go along". This is a wonderfully honest assessment, and it started me thinking.
It's probably too obvious to state, and at the same time too simplistic, but I think there's two big things involved in understanding social media - one is people, and how they behave as individuals and in groups (psychology, sociology, anthropology ...). The other is the medium, in this context, the applications built to interact with social networks. Understanding this part involves understanding the dynamics of networks (mathematics, physics, ...). Of course in saying this, I'm not considering content at all, which is one of the things that makes this simplistic...
Both the social and the network side of the subject are hard. We have intuition and understanding of both, to a greater or lesser degree,
from living in our physical / social world. But as soon as we start to ask hard questions, we run into substantial difficulties.
Our intuition is frequently bad when it comes to network problems. Just look at how common and successful pyramid schemes are - these all work because most people simply don't understand that their local understanding of their network doesn't extend easily to describe the global topology.
Similarly, the sociology of groups is extremely subtle and surprising - looking at analysis of election results shows how hard it can be to predict outcomes in such 'experiments'.
Given the relative newness of the technologies, my hunch would be that there are truly few people in the world who have risen above merely
possessing a collection of prejudices and a bag of tricks, to anything resembling true, wide ranging expertise. Dustin Wax has a nice, succinct writeup on expertise that I like, very relevant to the discussion here.
One of the interesting qualities of expertise that Wax lists is authenticity. It strikes me that there is a rather fine line between a social media expert, then - someone who is an authentic, potent manipulator of social networks - and a pathological liar. I'm not saying they all are - just be careful what you wish for.