Let's say you have a small size site with good users. You want to grow the site but not at the expense in the quality of users.<p>You want to add features which will make the site more interesting (like Reddit's article voting system) but you definitely do not want the site to turn into another Reddit.<p>You also don't want to do stuff like create a membership committee and a bunch of red tape to join the site.<p>What options are out there?
It really depends on the service, but basically comes down to promoting desired behavior (in this case quality content, be it posts or videos or whatever). Find some way by which quality can be measured (e.g. upvotes or moderation) and award users accordingly (e.g. giving more permissions based on upvotes/reputation, or hand-pick featured content). Optionally, discourage low quality content as well.
Have a browse through Meatball wiki. Although it's aimed at wiki style communities it has relevance for many others.<p>(<a href="http://meatballwiki.org/wiki/" rel="nofollow">http://meatballwiki.org/wiki/</a>)<p>You need to force good behaviour. Avoid "vested contributors". Meta is usually death; have some kind of separate channel for meta nonsense.