James Robertson has point out the obvious weakness of wiki tools: Wiki markup has no future:
The lack of WYSIWYG editing is a big barrier to adoption within organisations, and on the wider web. There are only a limited number of users that have the time, skills and inclination to learn wiki markup. It’s a fundamental usability problem, and the spread of wikis will always be niche as long as wiki markup remains.
This is a rather heretical point of view among wiki aficionados, however it is right on the money. If the outcome of using a wiki is to make content creation easy for a distributed group, wiki markup gets in the way of achieving that outcome. Most people can use a WYSIWYG editor if they have used a word processor in the past. This covers most Web users, especially in a corporate environment. Using obscure text code is an unnecessary and anachronistic hurdle to put wiki users through.
C. David Gammel, CAE 
Fortunately, most of the wiki vendors get this, and about the only place I see wiki markup language anymore is on Wikipedia. And I’d advocate for keeping wiki markup language over there. The barriers to entry need to be somewhat high.
James posted a follow-up to his original post with a reader’s comment that migrating wiki-style mark up (even those with a wysiwyg front end) to a traditional CMS can pose conversion challenges that you don’t face with HTML-based content. One more problem with wiki markup from an infrastructure and content re-use standpoint.