There are basically three kinds of people in this world - ones who know what Arduino is, ones who don't, and ones who find Arduino interesting but don't know where to start. This book is written for the people in the third category. This includes me.
The format of this book is very different from the regular O'Reilly books. It is written by a geek for geeks. So it doesn't start with a smooth introduction about the basics. It seems to have a rocky start since a lot of assumptions is made about the reader. The diagrams also seem to be hand-drawn on napkins. Chapters 1 and 2 contain a bit of what the author self-admittedly confession to be "fluff". Things start getting interesting from Chapter 3 where the author covers installation on the different OSes and how to figure out connecting the board to your computer.
Chapter 4 really rocks. I think I finally got what Arduino is in this chapter. I immediately ordered my Arduino UNO since I got the hang of it in this chapter. Chapter 5 takes you to the next level by talking about advanced I/O. The author keeps your interest piqued by informing you about the various I/O sensors that can sense the environment. Chapters 6 talks about some advanced circuits using a breadboard, components, and some wires. Chapter 7 ends the book with troubleshooting techniques. Appendices at the end of the book provide reference material for breadboard, reading resistor and capacitor values, and Arduino programming reference.
Overall the book is excellent for getting started with Arduino. It has rekindled mlove for microcontrollers that I hadn't touched for the last 15 years since I pursued a career in Java development. It inspired me to buy an Arduino UNO board and I hope to nurture the interest in electronics in my kids by showing them and let them do stuff as well.