HTML5 Up and Running is Mark Pilgrim's book on HTML5. The entire text of the book is also available at DiveintoHTML5.org. Just like the other books written by Mark (Dive into Python, Greasemonkey Hacks), this book will serve as a very comprehensive introduction to the topic.
The book begins with history of HTML specification starting from conversations on www-talk mailing lists to formation of W3C and to WHAT Working Group. Then it moves on to Feature Detection, high level view of new features - canvas, video, Storage, Web Workers, Geolocation. The next chapter is a dive into details of the Document elements, new semantic elements. The next few chapters cover in detail each of the new features - Canvas, Video & Audio, Geolocation, Local Storage, Offline applications, Form semantics, Microdata. Each of these later chapters can be read stand-alone without depending on others.
There are some open source projects mentioned in the book - Modernizr for HTML5 feature detection, geo.js for smoothing out differences over gelolocation APIs. These pointers should be of great value to developers.
The book website is itself a great study in HTML5 with its very detailed attention to live examples, typography. Great work by Mark once again and kudos to O'Reilly for allowing full version (which is in fact more up-to-date than the printed book) online and also for selling the ebook in DRM free formats!
Disclaimer: I am writing this post as a part of Blogger Review program. I am not being paid to write this review. But I received the ebook free for doing this.