Most of the notebook tools out there are focused on the writing.
They use the expression "note-taking" and that's... telling. And why I've taken to speaking/writing about "note-making" — I don't want to be always in the position of a consumer, always just writing down (summarising or recasting in my own words) someone else's thinking (though there are times I do!) — I really want my notebook/slip-box to be a collection of my own thinking and observations (no matter how half-arsed, ill-formed or partial).
And that's Leg One of what a wiki is about. Writing down the thoughts and linking them together.
Leg Two: It's also a tool for reading, organising, arranging and rearranging those thoughts. A tool for stimulating more ideas and thinking. As a tool for reading and rearranging there are more affordances it wants, and the current crop of notebook tools fail utterly at that.
This is also the place where wikis have failed me as a group-thinking/collaboration tool. Leaving aside the sort-plausible idea that people don't like to read, it's conceivable that the tools just make reading too inconvenient or ill-afforded. Then, too, if we start editing a page, or doing some deeper rearrangement of the text on a page, there's a lingering feeling that you're hacking on someone else's precious words, and there's something in us (if we're well-intentioned collaborators) that that's somehow quite offensive! It feels like a violation of the other person's being. (Does this speak to how much our words are a reflection of our inner thoughts and spirit?)
Then there's a Leg Three: we want to comment on one anothers' words; we want to have conversations. So [[WikidConversations]] are the next logical extension of what the tool wants to become. And no wiki or discussion forum or computer-based commenting system seems to have been very good at that. (Google Wave might have become good at that if it had ever had the chance to experience prolonged sunlight.)