We're using a large tikiwiki system for our student server at the University of Applied Sciences in Dortmund, Germany.
Anonymous users can only browse information; registered users can configure their Email and Webspace account via tiki. Registration is only available to students of our university. At the moment we have about 3000 registered users and 13000 potential users (known students in our database). Our tikiwiki was enhanced with LDAP authentication and several pages to manage personal preferences like email forwarding, homepage settings and so on.
Feel free to visit our site at http://www.stud.fh-dortmund.de/ (the site is entirely in German and most content is related to students at our school)