I have no experience running a site centered on user generated content, but it seems to me that the biggest problem/threat to any of them is the people who start showing up once it gains traction and becomes more popular.
Early users are a different band of the population, on every successful platform from StackOverflow to Uber they create a particular culture which is impossible to maintain as the general public arrives in large numbers.
Early users are a different band of the population, on every successful platform from StackOverflow to Uber they create a particular culture which is impossible to maintain as the general public arrives in large numbers.