I have one and like it. It just offers a lot more detail than the other options out there--sometimes to excess ("how to remove a tire in 57 easy steps"). Yeah, it's expensive, but I've found it to be worth it as I'm confident that I know what I'm doing between their instructions and the component manufacturer instructions that are on the web. (I'm not really a mechanical whiz). By following it, I end up good results, not just good enough. The writing is most certainly not interesting and it doesn't make for good bedtime reading, but it is clear and helps get the job done correctly.
The other cheaper books (and even cheaper websites like parktool.com) that are out there are quite good when it comes to making adjustments. If you want to do pretty much all of your own work, however, I'd recommend the Barnett's--the fact that's it helped me do more complex jobs on my own has meant that I've saved a lot more $$$ than it costs and I have a more well-tuned bike to boot. YMMV of course.