This isn't dead-on wiki-related, but ficlets is a cool new collaborative writing site -- you can submit a microstory of up to 1024 characters, and other people can write prequels and sequels, building sprawling nonlinear (and commons-licenced) narratives. It's from AOL, of all companies, but it's so well thought-out that you'd think it and AOL would explode on contact like matter and antimatter. (I'm helping write a cyberpunk programming firefox fanfic about a mad scientist type.)

In other gadgetry, Wikia just launched what it calls Wiki magazines, which basically seem to be wikified versions of digg -- instead of pointing offsite, the voted-on links go to on-site stuff. Neat stuff.