Have you browsed the wiki here? Honestly, between the wiki and the forum, I'm not sure why you'd need a book. Most people here are more than willing to share their knowledge. -Rod-
Save your money and DONT buy this book. I saw it at a local Borders. It has nothing much on scanning you will be disappointed. INstead, support this site and get the info from here or read some of the better magazines like Scanning USA and Scanner Digest.
I have it and have found it useful as an aid to explain things like trunked systems to friends who are new to scanning and are interested in knowing more. I suck at explaining stuff, so it's good to have the basics in writing to show people.
I find those "For Dummies" books mildly entertaining but I wouldn't waste my money on one. When it comes to a knowledge warehouse it's like they say, "Boy, you've come to the right place." and like the park sign says, "You are HERE."