I think HN fits this to an extent by weighting voting power according to account age and other factors, which would dramatically slow the speed with which an explosion of new users would change what is seen on the homepage. User comment quality remains a hard problem to solve though.
I find myself continually amazed at how HN continues to be one of the more overall generally "sane" discussion forums in existence. Still by far just about my favorite source of interesting links and equally interesting discussions about those links. "Kudos", "props", and "mad respect" at all those folks who help it stay that way.
