Mediawiki is pretty complex, but obviously very powerful. It is also very well documented.

I solved the spam problem, which was turning into quite a nightmare, by using a bridge between the vBulletin and Mediawiki software which set the various user permission levels using an interface I knew well - the vBulletin interface. It can be done directly in Mediawiki, but is nowhere near as user friendly as with this bridge.

I see there is also a phpWiki - but I've got no feedback to give on that.