Derek Huether has a post at The State of Agile that crystalizes the discussion of Agile Projecy Management (at least for me).
I surprisingly discovered that customers really didn’t care how I managed the project, as long as they got what they wanted, when they wanted it, at the price they agreed to.
This is a completly logical approach to project management and the use of a method (any method) to mangaginf other peoples money.
But what if the customer DOES care about how the project is managed? Now what? Care is needed to seeprate the argument. In the world where the customer does care about the method, the customer getting what she wanted AND staying on schedule and budget, AND knowing how the project is going weekly and for sure monthly in units of measure meanigful to the customer just may require folliowing a processes.
Now - once again - PMBOK is NOT a method or a process - no matter how many times some try to paint is as one. And things like PMBOK provide guidance to what activities need to be performed somewhere in the process.
So keep this in mind when you hear "the customer doesn't care how I manage the project, as long as they get what they want." Really? How big - or small - does the project have to be for this to be the case? What business or technical domain has to be present for this tp be the case?