Mike Davidson of Newsvine talks about User Generated Content

You must provide tangible benefit to users for their participation.

What’s not working:

• Services that require user participation to get started. Get people to square 3… etc before requiring to register. (Carl Sjorgreen Said almost exactly the same thing.)
• Buying users.
• Social networks for the sake of social networks.

What IS working:

• Letting users do as they please – The user is in control.
• Be open to people using your site in other ways than you intended.
• Let people contribute when they want to contribute.

The Dunbar Number (Robert Dunbar) suggests that the ideal size for healthy groups is 150 people or under. Too big can be too daunting. Provide ways to cultivate small groups.