Wikis are pretty good.
I think this is all a bit like arguing that a blog isn't a good place to enter structured data. The entire point with a wiki is that you don't have to be concerned with markup. The reason I like using a wiki rather than HTML is *not* because I can't write HTML. It's the same reason I use Perl to solve some problems and C++ others. I can jot down a couple wiki pages, come back a couple days later to polish them a little, then leave it alone. It's mostly unstructured text, with some simple cross-links, very little markup at all. Wiki cross-linking is tons simpler than footnoting, much simpler and it wouldn't be worth entering in the first place.
Having to laboriously markup text is a _barrier_ to capturing certain types of knowledge. It doesn't matter if the markup happens via HTML, XML, or nice pulldown menu items. Markup forces you to invest time in work which doesn't help you in the prototyping phase, which means that people won't brain-dump their _current_ understanding of things, because it doesn't look "pretty".
The only thing I wish was better was integration with other specialized solutions. I want a wiki integrated with a blog (not a blog mode within a wiki, or a wiki mode within a blog). And Sparrow. And other stuff. Let's call it "Notes" :-).
[I "get" blogs, but they aren't that exciting to me, they don't solve a problem I have - though they are certainly fun. The wiki concept does solve problems I've had for _years_, and I would no longer feel comfortable trying to work without one.]