One theme that comes up a lot in the book is understanding who is using your application. Right from the first chapter it starts with finding out who your user is and what is the job they are trying to do. Besides research, testing an interface and getting feedback is a constant subject, a lot more than many other interface books seem to focus on. Like Neuo Web Design, there's a lot of psychology cited and weaved into this book. One aspect I liked was how it used examples from many different areas, such as computer mice or video games in later chapters. In fact, learning from video games comes up at several points in the book.
A big part of this book is on how to test designs before writing any code. In fact the whole "Implementation" section is mostly about designing tests and collecting information. It's pretty in-depth and covers a lot of information that isn't usually found in books like this.
There are of course chapters on making interfaces functionality discoverable and consistent, which is expected, but there's also chapters on writing for the web and how readers hunt and scan pages for information rather than read them as they might a newspaper. Another chapter covers an idea that is known to designers but not really covered in interface design: simplifying and knowing when to leave things out. Of course, tablets are covered in this book too, focusing on the non-obvious differences between a touch interface and a mouse interface such as how easy it is to reach buttons on a screen. Each of the chapters are fairly short (5-6 pages) and there's usually some illustrations or black and white photos to illustrate topics - a bit sparse but makes reading quick.