Here is the backstory from his blog:
This morning, Jane Friedman (editorial director of Writer's Digest Books) asked me to pass along the following message that she also posted on her blog (http://blog.writersdigest.com/norules). Please feel free to comment below if you have any feedback to share on this topic. Thanks!
In the original message, Jane explains that the project of a book about writing and critique groups was tabled by the sales people because they want to see hard evidence that enough people are in writing groups (enough to buy the book) and whether those people would spend money on a book about writing groups. So she wants to gather information on how many people participate in writing groups.
You can go to the Poetic Asides blog post or to her blog to answer the question.
Here is the answer that I posted on PA:
I've been a part of a writing group since 1992 (we did have a five year gap around the turn of the century).
But I don't think that's the right question. It isn't how many people are in writing groups, but what do they need that a book could give them? My group meets to critique poems, and while I'd be interested in hearing about what might compel me to buy a book, I don't know what that would be.
Some groups meet to write, so a book of prompts might be helpful, but I think there are quite a few out there already (not to mention prompts on poets' blogs and websites).
Are people in groups your audience for this project, or is your audience really the people who would like to be in a writing group but haven't been able to find one or start one locally or online? In that case, you want to find out how many people share that need and what you can provide in a book that will fill that need.
(Maybe the best way to connect with your audience isn't through a book, or maybe it's a combination of a book plus other things, like an online directory, a sort of match.com for poets.)
Just my thoughts.