User blog comment:Sarah Manley/Announcing Achievements - Edit your way to the top/@comment-1264394-20100810162516

The Fairly OddParents Wiki has these and they've really helped increase the activity. New editors and previously semi-active editors have helped eliminate uncategorized pages, red links, and have halved the amount of stub pages.

I've seen some bad from it too like useless edits, spamming, and cheating the system, but I think as long as the admin staff keeps its Wiki's users occupied with new pages/projects and sets an example to their members on how to style their pages then this add on should be beneficial for your wiki. There is also no reason a small wiki (less than 1000 articles) should have this, since your users will run out of pages too quickly and will start "competing" for edits, unless your wiki is completely dead and needs any form of stimulus it can get.