I think the book is a must. While a lot of info is covered in the forums, the answers are from non-experts. While we may have personal experiences we would like to share, our own recipe for progress is not nescesarily going to work for everyone else. The book provides easy reference to ojective, error-free information on all subjects concerned with PB living. Relying on just forum posts for your diet information would be unwise, in my opinion. The book is packed with information, and I read and re-read sections regularly, and often learn something new with each read or two, or come across something I had previously forgotton.
It also functions as a tool to help you actively participate in the forums. By being confident in your knowledge of PB, you can be sure that youre giving out good advice to others.
I honestly dont know how people get by without the book.