Rick Segal's post is a good snapshot of the response to writeboard.
Personally I love wiki. And I want to see the wiki idea and name become as widely known and adopted as, say, "blog". So I'm not really into brushing "wiki" under the carpet as too geeky for ordinary people to understand. (Which is, naturally, why I named my program SdiDesk and not something obvious like wikipad, wikinotes or uga-uga - doh! :-( ).
37 Signals are a smart company. They have a genius for doing one little thing (that often seems trivially obvious) in a very usable and user-friendly way, and turning it into a massive hit. So it's not surprising they're coming in to disrupt wiki (and JotSpot) with a simpler-than-you-can-possibly-believe one page, wiki-like thing.
It will be interesting to see how it takes off. What strikes me, is that they've removed what seems to me to be the wiki "essence" : the ease of creating multiple pages and links between them via concrete page names. And, of course, what most people remember : unrestricted access.
What's left is a little bit of wiki-markup. Plus versioning. And the fact that this is a collaboratively editable document.
I wonder if they'll subtly introduce multiple pages with links between them at a later date.