I am interested to know what people think about all these PhD guide books. Has anyone found them useful? I suppose a lot of the info in them can be found on forums like this.

I haven't read any PhD guide books. But, I found a lot of resources around PhD life. The one I recently read and I consider it as a good guide:
www.cse.ucsd.edu/users/mihir/phd.html

I liked "The Unwritten Rules of Phd Research" by Gordon Rugg and Marian Petre. Fun to read, and useful.