Hi Willemina,
I quite like the MediaWiki engine, but like you said, it is often not recommended for smaller scale enterprizes. I heard once that there is a lot of code behind it which is purely there for making sure it works with HUGE traffic, ie: it works across multiple servers etc. I'm not sure if that is true or not though.
At my work, our computer admin installed
WikkaWiki for us to try out, but so far I'm not impressed. It has lots of things which I consider bugs - although they are intentionally designed into the software.
It seems that Wiki software simply isn't as well developed as forums and blogs are.
The main thing we need at my work, is an idiot proof system which people don't need to be taught how to use. If someone needs to remember something to use it, they probably wont! So the most important thing off all, is that the software is 100% intuitive. Some of the wiki programs out there are far from intuitive and even good old Wikipedia fails in some ways due to know special Wiki code to achieve certain effects.