I moved to TagglyWiki as the main documentation format for NHibernate Query Analyzer about a week ago, but only now I begun to take advantage of the tags ability.
For instance, I've a bugs tag that I use to mark all of my open bugs, and now I don't need to save them in the same tiddler (which would very soon become huge). When I fix them I only need to tag it as fixed bug and than is it.
I'm liking it more then more I'm using it. Truly a wonderful thing to have, and the WikiFormat is easier to learn (for the day to day stuff) than HTML, or even using GUI to do it.
[Update: Here is the latest version, so you can see for yourself, the Wiki on the repository. I love Subversion.]