I kind of like Wikis for some applications, but I’ve found quite of few of them to be a pain to setup (current easiest in my experience has been phpwiki). I also haven’t seen an easy way to setup multiple ones (I get one for personal writing, I can flip a switch and give a friend one for a book she’s working on, etc). They allow for instant editing on the web in a way that is in many ways easier than even blogging (but yes, it does have its idiosyncrasies).
I know wrapping your head around the idea of a wiki isn’t the easiest thing (it took me many months between the first time I was exposed to one, and the time at which I found any use for them). Still, I’m surprised there isn’t any sort of single community host for them. It seems like something I’d give someone five bucks a month for, to let me run a wiki that was instantaneous to sign up and get going.
I could also see wikis used for specialized purposes, and I wonder why special flavors haven’t popped up. I wrote a book with two friends, and we frequently exchanged ideas, lists, and built up the book’s glossary on a wiki. It was the perfect place to go and jot something down at any point in the three month-long book writing process, working great as a collaborative idea pad. I could see it used by screenwriters as well. Start a list of funny jokes, set aside another page for subplot ideas. When the inspiration strikes, expand your list of jokes page into dialogue between two characters. Then expand the page plot ideas page into an outline and link to a scene in the larger script, which is the joke page.
It took a while before there was a free blog host like blogspot to let anyone blog in minutes. Maybe I missed the free wiki host that allowed for much of the same thing.