I've mentioned Mike's work previously on explaining Agile to a PMI certified person. He put up a practice post on the evolution of a GANTT chart into an agile project plan. He's not at all endorsing the use of GANTT charts, but he's correct in assuming that we have to speak the language of a PMI certified person to help explain the philosophies of agile. It's a good read and it has expanded on my tools for helping explain this stuff. This post was his way of flushing out his thoughts for the upcoming Orlando conference, so I'm sure he have even more to say in a few days after the conference.
Update: Here's a link to his final post which also links back to all prior posts in this thread.