I would like to thank Michael Haupt, Nicolas Cellier, Hannes Hirzel and Casey Ransberger for investing their time in this discussion. I agree with what has been said so far, but perhaps we should step back a bit and try to define what will be the scope of the documentation and how it will be presented.
About the who, I fully agree this will be a job for everybody and not just the Documentation Team. I see a team like this as a group that will create the necessary infrastructure and might even act as editors, but the authors are a separate group (it will be great if people want to be a part of both, of course).
Of course we have methods comments and class comments, but I think there is no limit to the kind of in-image documentation we can have. And if the trend is towards a smaller kernel with loadable stuff, the bulk of this documentation could be in the form of loadable packages. Using the same tools and proceedures as for evolving the code is certainly a good option (though this might require extending those tools a bit).
One important feature for the documentation is to make it more easily available outside of Squeak. I don't like to write the same thing twice, but imagine that we could create a doc.squeak.org site running a fully loaded image and automatically exporting all the documentation in a form that people and web crawlers can use.
These are just some ideas to keep the ball rolling.
-- Jecel