Wilson (the main author) has worked on Sun's Swing team and then on the performance team in the late 90's and that is where he draws his experience from. This book is not geared toward people that do server-side Java (which I believe to be the great majority).
Since this book was from Sun Press I definitely expected more from this book considering the depth provided by other books from them. But this book embarrased me by reiterating the tricks already known and introducing the esoteric concept of benchmarking and not providing much details with it.
Being a java developer since last 5 years, I didn't learn anything new from this book except the concept of benchmarking which this book brushes lightly without really explaining it well. Sincere advice: Don't spend your money on this one.