Leaving aside the sites that are not communities, you have Youtube (got big because of lenient enforcement of media copyrights), Craigslist (got big because it

Leaving aside the sites that are not communities, you have Youtube (got big because of lenient enforcement of media copyrights), Craigslist (got big because it allowed all kind of stuff, up to and including prostitution), Twitter (people complain about Twitter lack of management on HN weekly, and it never turned profits). The only exception from the rule is Facebook. Zuck's running a tight ship over there and it did beat "unmanaged" Myspace.