I am a big fan of Wikipedia, using it extensively as a way to provide depth to my online writings. Aside from being a useful tool, Wikipedia is very interesting as an experiment in social software and (prospectively) knowledge engineering.
Thus, I am quite intrigued by the efforts to extend it into a Semantic Wiki, as documented on the Semantic Wiki State Of The Art page on the Semantic Wiki Interest Group web site. I like the fact that SeMediaWiki explicitly starts from a user-centered perspective: how do we create a semantic wiki without losing our readers and editors. That said, I think there will be plenty of room for assorted hackers and ontologists to add complexity, behind the scenes!
I am currently working on a specification for Ontiki, an "ontology-aware" wiki which I hope will be useful in Model-based Documentation. See my home page and resume for general and professional information.
I am in the process of creating a set of pages to document the MySQL table structures that MediaWiki uses. See MySQL Tables.