This book is the reference to anyone who wants to make good use of CSS for webdesign.
I didn't have much knowledge of CSS when I started reading it but found it quite easy to understand. Every property is covered in detail and, although Eric doesn't focus on browser support, it mentions compatibility issues on the most relevant properties and behaviour of different browsers.
The Box model and the inline layout are heavilly covered. This is the part where I found the book a little harder to follow. Floating rules are very well explained.
Through the book, Eric throws in some very simple examples to illustrate the use of one or another property. Don't expecting anything like a cookbook, though.
If you prefer the recipe type of book, this book isn't for you, CSS Cookbook would be a better choice. If you like to experiment as you go and check the results, then this is definatelly your ultimate resource.