Stephen Downes gave a presentation at the Canadian MoodleMoot and, after watching the recording, I wrote this post. In it, I reflect on the work he's been doing on groups vs networks for the last 12 years or so, and the mechanisms that best suit each of those.
I think that we need to encourage pro-social behaviours and to do that, people need 'skin in the game'. We can do that a number of ways, through badges, through reputation such as kudos, and through recommendation engines.
At the end of the day, I think we're going to have to try a few approaches and see what works in a Moodle context!