Why? Ease of use, simplicity, speed… and the right subset of features and a simple interaction model. It feels solid. It looks good. It does what I want it to do (I’m also watching Stikipad as it offers Textile).
And now it looks like I’ll even be getting to do some work for the team on some upcoming usability and design tasks. Not to mention microformats integration. Nice.
Bonus: So I’m curious — what features do you look for in a wiki? What’s missing from your experience? Essentially, if you ever had a wiki feature request that you’re dying for (or something you never want to see in a wiki again), what would you say?