Hello Hans, ayear ago (more or less) Ludo (NwikiTeam) launch a "survey" of wiki uses (but I'm afraid that was in the spanish forum: Moodle en Español) probably he has the information translated to english
Anyway, I post my newest use of WIKI: to create a WEBQUEST (I know there is a module fr this, but not in the standard distribution. And wiki is enought for mi fro this purpose)