These include many large public wikis, including Wikipedia.org, Sourcewatch.org, dKosopedia.com and Anarchopedia.org. Given the vast web traffic Wikimedia receives, such services are very well proven for high traffic applications. They support very sophisticated social network and content management functions on deployment.
Mediawiki is inherently troll-friendly though bad policies can make it less so. Wiki troll culture is largely a phenomenon of mediawiki based services. tikiwiki-based services usually employ aspects of tikiwiki that discourage the creation of any independent faction, and are far less capable of social network service functions on deployment.
Many specialized wikis including embodimentwiki.org, yoism.org, consumerium.org and wiki.creativecommons.org and memory-alpha.org also use mediawiki because they are facilitating similar dialogues or seek to become larger forums.