I must say: I enjoyed going through this book. It is written in an opinionated and slightly irreverent style, so I found it a mildly amusing read.
That being said: why do people buy a book on HTML5? Some would like to have a good in-depth reference on the ins and outs of the new language. Well now - that's not this book. Others might be new to web development and think learning HTML5 would be a good starting point. While they are right that HTML (5 or 4) is the place to start, this book surely isn't.
There's some depth when it comes to background, but much less when it comes to HTML5 itself or how to use it. True, the <canvas> tag and geolocation are covered pretty much in detail, but the author made some hard to defend choices in spending his paper estate.
HTML5 gives us no more than a handful of new tags, still some of those (<mark> and <section>, for example) are simply mentioned once and that's that. No examples, no advise on where to use them, nothing on browser support. Yet the book takes five pages at the start to tell the story of how the img-tag came into being some 15 years ago. Again, mildly amusing, but probably not the reason you are thinking of buying this book.
Another example: there are 10 pages with a primer on audio and video codecs, plus another 19 (!) detailed pages (with lots of screen shots) on how to use a number of specific and probably soon outdated software tools to encode video for the web. All fine for those who are completely new to video encoding and believe a book on HTML5 should be the starting point for that. But when it comes to the actual <video> tag (under the aptly named heading "At Last, the Markup"), this consists of a meager 3 pages that include a statement like this:
"The <video> element has methods like play() and pause()".
Huh? "Methods like"? So which other methods are there? And how and where would I use them? Are these standardized across browsers? Where can I find more about them? Any example, maybe?
If you think these are the kind of questions a book on HTML5 should answer, you are out of luck. The above sentence is all the information on this particular topic you are going to get. Not a word about implementing these methods, or on how to style the browsers' native video controllers that come with HTML5 support. There are a good number of external references for information on things like Unicode, codecs and video containers, and some useful scripts, but not a word on how we can get the information on how to control and style the <video> tag. Maybe the logical conclusion would be: in another book on HTML5, perhaps?