I've been watching MediaWiki for some time, and whined to the developers about the lack of database table prefixes. I'm sure it wasn't my influence alone, but within a month, they were there in the 1.4 beta! I've been using several of the betas since, with excellent results -- they are very stable. There are two active mailing lists -- one for users, one for developers -- and the main developers are very accessible.
MediaWiki has a nice extension mechanism where you register a PHP callback with a unique HTML-style tag. Then it delivers whatever is within the tag-/tag pair to your callback, which then produces HTML. This is hobbled by multiple caching mechanisms that essentially make dynamic content impossible. For example, I implemented a Unix fortune(6) extension: http://www.islandseeds.org/wiki/Test:Fortune -- it was very simple to do, but it only shows the same fortune over and over! There needs to be a mechanism for disabling or manipulating caching.
Otherwise, I'm quite pleased with MediaWiki, and am going to jump on the non-beta 1.4 release the instant it happens. (Currently running beta 5)
(Bragging rights: I worked with Ward Cunningham in the '80's at Tektronix Laboratories before he invented the Wiki concept. Ward is an amazingly prolific 'idea generator!' Anyone interested in wiki philosophy needs to visit his site at http://www.c2.com -- the ORIGINAL wiki, still running!)