When the XNA 4.0 Workshop first began back in January I did a survey of the available XNA books. At the time, there were very few XNA 4.0 books available, and even among the 3.0 books there weren't many that I felt covered the topics in sufficient depth and in the correct order. After careful consideration I ultimately chose XNA Game Studio 3.0 Unleashed as the "textbook" for this workshop.
Unfortunately, the book covers XNA 3.0, not 4.0 which has made it difficult for people following the workshop to get projects functioning, as there were several breaking changes between XNA 3.1. Additionally, after eight months, the AppHub has come a long way in providing additional resources for those wanting to learn XNA 4.0.
So my plan moving forward is to, in the weekly workshop introduction, identify the topics we'll be covering for the week, point to a few resources on the AppHub which may help, identify some documentation pages in the MSDN Library, and then wherever necessary write additional tutorials to supplement the information already available. Also, I will indicate which chapters in the textbook we'll be looking at for those who purchased the book and would like to follow along that way.
What this ultimately means is it doesn't matter which XNA books you have, or if you have none at all. Hopefully by addressing the topics, documentation, and tutorials already available I can make the workshop more accessible to everyone.