WackoWiki

View source for Re: How many sites are using wackowiki?

There was once a page for this, the issue with the list was to keep the list up to date and relevant.
Most wikis are deployed in intranets, others are non or semi-public. Any user is allowed to leave a link to his wiki(s) on his profile page. Others may be don't want their wiki exposed as such.

A good idea is to categorize such a list by language and application area, preferably with a few selected websites which can serve as good examples.

some use cases
  * documentation
  * community web site
  * life role playing
  * course ware
  * web site
  * CRM 

It's quite a challenge to categorize them all. So yes such a list is on the wish-list, you can start one if you like.
Regarding the mere quantity of deployments or daily users it is hard to judge.