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, expand2