The accessibility guidance on this DVD is probably no more than a reasonably-experienced person ought to already know. Where it shines is in the basic principle that web pages should be beautiful and useful both when displayed normally and when filtered through an assistive technology. Clark is best when telling you what NOT to do (because a screen reader can already do it) and how to incorporate semantic information while making the page more beautiful for everyone.
That said, you will also learn more about accessibility. Do you know how to mark up a complicated table with multiple nested levels of headings? Or how to show an image and its description beautifully for normal browsers, screen readers, AND browsers with CSS turned on but images turned off? Well, you'll learn here.
I especially appreciate the author's clear passion for accessibility and his rousing statement that the test of professionalism in a web designer is that they make the experience as good as possible for all users. I feel inspired to go out and build a beautiful, accessible web.