This is a book for people who want to use FreeBSD as a server -- for mail, web services, DNS, etc. It's not a book for those who want to use FreeBSD as a desktop machine. FreeBSD makes a perfectly good desktop OS, but Absolute BSD includes very little information about setting up X or installing and using desktop applications. If you want to try out FreeBSD as an alternative to your Linux desktop, look elsewhere. But if you want to build a server, and learn an awful lot of incredibly useful bits about basic systems administration tasks (much of which is applicable to any other *nix system, including Linux), then I haven't found a better book for this purpose.
I bought this book because I liked Lucas's more recent book, Absolute OpenBSD, so much, and he covers FreeBSD at least as well, if not better. His writing style is humorous and very readable while still conveying a lot of technical information, and you not only learn what you need to type on the command line to accomplish a particular task, but also how a SysAdmin thinks.
Being more familiar with Linux, only somewhat familiar with BSD in general, I have gone from chapter to chapter and this book has guided me through installing FreeBSD both from CDs and over the network, upgrading it, and recompiling a more optimized kernel (which turns out to be a fairly painless process, if you follow the instructions in this book, for those of you who believe, as I did, that recompiling kernels is a big hassle, messing with the guts of your machine and likely to kill it if you make one stupid mistake). He explains every configuration file, how to set up (or turn off!) services, how to make your machine secure, how to make it useful, how to install and upgrade new packages, and how to provide web, mail, and DNS services, and his instructions are very clear and makes it much easier to understand WHY you need to do certain things as well as what you should do. Someone who has never performed any of these tasks before should have no trouble doing so by following the instructions in this book, and afterwards you should know enough that with a little exploration you'd be able to do the same on another OS.
As the author says at the beginning, this book is actually meant to be read from start to finish, rather than being flipped through as a reference guide. What you learn in each chapter builds on the one before. Thus, this book might be somewhat less useful to experienced SysAdmins who just need to know BSD-specific information -- while the information is comprehensive enough to make it a good reference guide, there is probably a lot of extra space devoted to material that experienced SysAdmins already know. However, if you're a novice SysAdmin or just want to learn how to run your own server at home or a small one at work, I think Absolute BSD does a credible job of turning absolute novices into competent junior-level SysAdmins. So this is really a book about systems administration, not just FreeBSD, though the material is all aimed at running FreeBSD systems.
For its intended audience (novice or junior-level systems administrators or people who just want a web server) and scope (using FreeBSD as a server), this is an excellent book. There are other FreeBSD books out there, or more generic books about Systems Administration, with a wider scope, which might be more useful for other purposes. But I would still absolutely recommend including this book on your shelf if you are going to perform admin duties on any system (especially *nix systems), or use FreeBSD for any purpose.