This book is in its third edition I've read somewhere and it won't be its last, even as Google is trying to limit the number of malicious searches very timidly (they could do much more) and even if Googlehacking is only showing a very limited part of the online vulnerabilities. The forum by Johnny Long that started it all isn't too active anymore and every exploit has now a Google search string adapted to it. Some worms even use Google to find infectable computers.
Some parts of the book may be dated, but it stays an essential handbook for the securitypeople around here. The most important thing is not only the copying of the lists with useful searches but learning to think like a hacker that is using Google to try to do some discovery searches. There are automated tools for some of the searches but it is only the human eye and mind that will find the little snippets that have to be put together to arrive at a Google Dork that may show you the list of vulnerable sites that you were hoping for.
PS It has some very useful scripts for Google hacking that you can install for your security work.