Dewar uses a publicly available resource, the New York Metropolitan Transit Authority Data Set, to demonstrate how the library can be used to present data in a number of ways. The book covers all the basics with D3, from the selection model, to interactive graphs, and specialized layouts, such as force-directed graphs. While it covers some of these concepts, it never goes into great detail about anything in particular. While this is a "getting started" book, it's very much an introductory title.
Still, this is a relatively short book. It's a good introduction to D3, but leaves a great deal about the library to be explored. In chapter 3, the author notes that the standard D3 visualizations are rendered in SVG, which limits the usage to modern browsers. While it is noted that Internet Explorer 9 (March 2011) provides SVG support, the book fails to explain exactly what that means today. As I've mentioned before, IE 8 is the most recent version of Internet Explorer that can run on Windows XP, which still has a sizeable market share. While there are workarounds, such as using d34raphael to render VML output in earlier versions of IE, or using svgweb to render the SVG output in Flash, these problems are glossed over with a simple aside.
In the end, D3 is a very useful tool, and Mike Dewar's book does a decent job of explaining how to go about using it. It's unfortunate that the book doesn't go into greater detail, especially since the book is so short to begin with.