Wikipedia has been experimenting with various “approval” mechanisms, and for the most part they were a failure (see Pending changes), mostly for reasons pointed out by Fredrick. Experienced editors feel reviewing of changes as a burden, and as result pending changes sit in a queue for extended periods of time, at which point they are more prone to cause edit conflicts and complicate workflow for those wishing to tackle them (who then give up).
What was a success at Wikipedia was the Cluebot (who used relatively simple rule set to revert obvious childish vandalism), and after that various measures to limit editing capabilities of new users (banning creation of new articles for unregistered users; blocking non-500/30 editors from many controversial pages, and similar).
Plus, there was always an efficient revert mechanism readily available for all registered users, who could revert vandalism on spot.
Obviously, our environments differ quite a lot, but we have some lessons to learn.