I think the factors that make, or break, an online community are: The number of active users, the visibility of posters (so reputation is at stake), and the abi

I think the factors that make, or break, an online community are: The number of active users, the visibility of posters (so reputation is at stake), and the ability for the community to self-moderate. There seems to be a magic threshold when the user base size crosses it and suddenly people are more disruptive. Based on my observation of a few online groups I've participated in.