Having used the Wiki plugin for a month or so now with 240 pages 53 categories and 100+ tags, we are finding a few bugs / oddities. I have to say first that in general it's very good / great.
1) When a wiki page is displayed the 'categories' associated with the page are displayed assuming there is only one category. So, if you have more than one category associated with a page they all run together without a ", " in between.
2) If you select EDIT to edit a page then a) categories are presented in a drop down list while b) tags are not presented at all. If you Edit a page this way and save it and you've more than 1 category associated with this wiki you only keep the category that's the highest in the list - you LOSE all other category associations and c) there is no way to select more than one category. This is a SERIOUS BUG. I'd recommend dumping 'Edit' and rename 'Advanced' as Edit.
3) Suggestion: It would be nice if there was a 'proper' discussion page rather than a comments list. A 'normal' wiki has a 'behind the scenes' editable page where people can discuss the page. A comments page is a poor substitute for this. I'd like a proper wiki 'discussion / notes' page and also the ability to have comments to. I'd also like to have an option to have the comments below the wiki page.