Apart from Wikipedia, wikis are used by no one. That is surprising because on the first look, they are an innovative example for a group ware software. It allows to edit documents in a team, all the versions are tracked and it's possible to use categories, images and a powerful markup language. To investigate why Wikis never were a success we have to investigate a potential use case in which the principle make sense.
Suppose a single user likes to write down his personal notes. Instead of using an outline editor, he is using a local wiki. The categories are equal to the sections and in the wiki the single user notes down keypoints. Such a use case make sense. Wikis have the same or even a better functionality like traditional note taking software. At the same time it gives a hint what the limit is. In most cases, a note taking software is used by a single person, but never by a team. Most of the existing note taking and outline programs are single user applications. The idea is, that only one person creates a personal mindmaps and fill it with knowledge. The reason is, that the written keypoints of person 1 doesn't make much sense for person 2. Even if he has technically access he is not interested in extending the notes of somebody other.
The normal communication form between humans is not with keypoints but with full sentences. E-Mails, books and memos are written in natural language. This format is expected by the other side. That means, a person makes personal notes for himself, but if he likes to provide the knowledge to a larger audience he has to convert the notes into sentences.
In theory, it's possible to fill a wiki with full sentences. But the advantage over a word processing tool is small. A small comparison can explain the situation:
- wikis are strong for note taking purposes which are based on keywords
- group communication is based on full sentences
Bascially spoken a wiki is able to replace stand alone note taking software, but a wiki can't replace e-mails or written pdf documents.