I've been for some time a great fan of eXtreme Programming. Even if most of the places I know that ponders using XP almost never implements XP completely.

From my experience of never implementing completely XP in some places, indeed, there's no silver bullet, but...

1. the Agile approach, in general, always argue for a constant negotiation between the customer and the developer.

2. the Agile approach, in general, argues to remove the bureaucracy implicit to the managing process.

3. the Agile approach, in general, makes the customer realize that he's paying for a limited set of resources and that he has the right to say what is more important, but he can't make a team work more than it can...

So, even never being in a completely-XP environment, I realize that these three values are something that really make some difference in accepting the view-changes of the customer and making the customer accepts the limits of resources they have available for them...