Though this is the 3rd edition, this is the first time I have picked up this book. As a proponent of the *BSDs, I appreciate have good quality material like this book available to overview and then get down into the mechanics of key subsystems, like PF.
I appreciated the clear, concise writing, as well as the multitude of real world examples.
One of the key chapters for me was Chapter 6: Turning the Tables for Proactive Defense. Peter goes in-depth into how PF elegantly handles issues like SSH bruteforcing, as well as how PF handles spam with stuttering, blacklisting and greylisting.
Highly recommended for someone that is interested in working with PF, or is already administrating PF, but looking for some extra help in certain areas.
-Josh
Defensive Depth 