A long, varied, well researched, and extremely interesting talk on group dynamics by Clay Shirky, whom I have just discovered.
A Group Is Its Own Worst Enemy
I find much of it rings true about some of the groups I've been involved in building, and there's much there that I had sort of intuitively guessed, but needed more data points on.
And so I'm glad this talk provided me with a lot more datapoints.
Actually, so many I think I need to read it again a few times to soak it all in.