I'm currently (02/2004) evaluating Tiki for use by our inhouse linux-based development team for documentation and team-building. I've used Wikis for a couple of years (starting with PHPWiki) but Tiki is the most sophisticated/featureful one I've used to date. The only thing I've found lacking so far is truly automated hierarchical navigation - unrolling categories/directories/structures in a sidebar would be lush.
I started with a ZX Spectrum way back when and have been using computers 210% longer than I haven't. More recently I've got a background in Search Engines and Content Management.