"Great opportunity for designers ... record their screen while they design"
According to Jason Fried of 37Signals:
Design Screencasts
I think a great opportunity for designers to generate revenue off of ‘waste products’ is to record their screen while they design. Whenever they’re in Photoshop, just hit the record button, and at the end, package up the video and sell it to other designers. That, I’m telling you, is a by-product that is worth money.http://carsonified.com/blog/business/make-money-off-your-by-products/
How could that work in book (or ebook or blog post or article) form? Simply focus on showing people what you do with simple commentary and explanation. Don't get too into figuring out what you need to tell people. In books as in life, actions speak louder than words.