I used to think that the great GM guides had great GM advice. But, man, I have read so much of the same thing over and over and over again... This is how to start a group, these are the different kinds of players, these are the different styles of games, this is how to deal with problem players...it's almost getting as bad as opening a book and reading, "What is an RPG? Well, have a seat, Timmy, and let me tell you..."
So, while I think GMing advice is useful to those that haven't roleplayed a lot in their lives, and a good campaign requires a lot more than knowing what crunch to use where, I just skim over those pages now, and look forward to a DMG that has less advice and more system.