In the past holidays I bought a few books about FreeBSD: Absolute FreeBSD: The Complete Guide to FreeBSD 2nd Edition, The Best of FreeBSD Basics, The Book of PF and Building a Server with FreeBSD 7.
I'm pretty happy with all of them and I recommend them, under certain criteria, to anyone looking into FreeBSD. Why under certain criteria? If you're looking for a book on desktop usage of FreeBSD you'll find The Book of PF pretty disapointing.
Absolute FreeBSD: The Complete Guide to FreeBSD, 2nd Edition is the perfect combination for FreeBSD's own Handbook. At times the Handbook might seem too straightforward by not offering advices or sharing experiences. Michael Lucas' Absolute FreeBSD on the other hand presents the reader with rich information, background, advice and reasoning although focusing on the network administrator and setting aside the desktop user.
If you are looking into a nice FreeBSD book to get your feet wet on Unix-like systems so that you can carry out mundane desktop tasks then I'm afraid that Absolute FreeBSD simply isn't for you. If you on the other hand enjoy FreeBSD, know Unix basics and want to expand your horizons and maybe setup a personal server and even make a living out of FreeBSD, Absolute FreeBSD is definitely for you.
I don't have an IT background though I know my way around Unix-like systems so I've found chapters like Chapter 6: The Network extremely useful to cement some disperse concepts that I have (had thanks to Lucas' book).
People new to FreeBSD and Unix-like systems in general will find the first two chapters filled with helpful advices on how to prepare yourself for the tasks of installing FreeBSD and seeking help, especially the Preinstall Decisions section. To help explore FreeBSD Chapter 10: Exploring /etc is simply golden as it goes over the files available in /etc while describing what each does.
I found Chapter 3: Start me Up! The Boot Process very insightful. Chapter 4 brought RCS to my bag of tricks. The security chapters (7 and 9) were also very interesting reading namely the part regarding Jails.
Personal favorites were Chapter 5: Kernel Games, Chapter8: Disks and Filesystems, Chapter 11: making your system useful, Chapter 12: Advanced Software Management, Chapter 13: Upgrading FreeBSD, Chapter 18: Disk Tricks with GEOM. These are the chapters I'll ended reading time and time again and are largely FreeBSD focused.
Chapters 15 and 17 focus on adding services to FreeBSD and go over SSH, FTP, NTP, Inetd and Apache web server. Pretty useful as I'm planning on setting up some personal web serving stuff.
I'm not much into email and DNS stuff so I didn't payed much attention to chapters 14 and 16, however if the reader is into the subjects I'm sure he'll find both chapters very important.
Props to chapter 20, 21 and the Afterword expand on what FreeBSD is, what it can be, how can you interact with it and what can you do to improve it.
To sum up, just go out and buy the book. It's worth every penny and more.