You are right John, the skinning elements have not been touched much but I believe the second book was a follow on from the first, the same authors involved, and their knowledge of skinning perhaps wasn't as great, afterall, it's evolved to be a subject on it's own.
The DotNetNuke for dummies book will have some elements of skinning, but I wasn't asked to participate - Scott has a colleague he's perferred to work with and it's not at the level of information you're looking for anyway when it comes to explaining the topic more deeply.
I have been contracted by Wrox to write a book which is called Beginning DotNetNuke Skinning and Design, which I'm currently writing. There are a two chapters within the book which are written by two others. It will be covering the topics you have mentioned and others and I hope will be the handbook for everyone who wants to understand skinning and design in more detail.
Also, we are about to do a soft launch on a new subscriber based site, where I have partnered with 2 others (managing this is just too hard for one person) where we have put in place some hands on approach articles. It will be covering areas that you mentioned and also other topics not covered in the book.
The book has the words "skinning and design" since I believe they are related. I was asked early last year to write a book, but I really felt that I didn't quite have enough history, but 18 months later, still working in this space and learning every day, I felt it was something within my scope to take on.
Being able to work with developers to assist them in the integration of their module to websites is something I enjoy doing too.
Thanks for sharing your thoughts in this area.. and you'll find with dnn or any other application you become passionate about, there's something new to be learnt every day.
Nina Meiers