Here are a few places where you can see Massive Wiki being used.
The Tools for Thought Map project is using Massive Wiki to develop their map.
Jordan Sukut is using Massive Wiki to help organize the Lionsberg project, and he is also writing several books inside the Lionsberg Wiki, linked from the Jordan Sukut page on Lionsberg Wiki.
Jerry Michalski is using Massive Wiki for the Rel8 website.
bandstands is Bill Anderson's personal wiki.
Peter Kaminski's personal wiki/website is peterkaminski.wiki.