This is pretty old (from a 2003 keynote), but I hadn’t seen it. A Group Is Its Own Worst Enemy:

Good morning, everybody. I want to talk this morning about social software …there’s a surprise. I want to talk about a pattern I’ve seen over and over again in social software that supports large and long-lived groups. And that pattern is the pattern described in the title of this talk: “A Group Is Its Own Worst Enemy.”

Via gapingvoid