I had pre-ordered this book and received it yesterday - it took me just over an hour (the duration of my commute into NYC) to zip through it. Based on this, my quick review.
The book is a slim 86 pages. Given the amount of detail in the HTML5 spec, this may seem lightweight. And in fact the author does spend the first 2 (of only 6) chapters discussing the history and process behind the creation of this spec - which further unsettled me. BUT.... once you get to Chap 3 (Rich Media) through 6 (Web Forms 2.0, Semantics and Using HTML 5 Today), you immediately derive a benefit from the brevity.
I see this book as an HTML5 buffet table. You can get a quick taste of all the different flavors and features that make the spec so compelling to web designers -- and then given sufficient tools and pointers for those who want a vertical 'dinner' on the aspects of primary interest.
The key takeways for me:
HTML5 favors practice over theory and, as the author puts it, "paves the cowpaths" rather than trying to forge a new road that will require a new learning curve from web designers.
Transparency tops lock-in. This should make rich media content easier to search, index and manipulate by not only making semantics visible but making every interaction with that content observable to the application.
Adoption is quite risk-free. While browser support is not yet ubiquitous, the author explains a few ways in which designers can get to evolve their web applications while still playing nice with browsers that are yet to catch up.
Summary: Loved the buffet. Now going in search of a week long series of dinners.