Craig Brown pointed out the Harvard MBA Oath
Josh had a question awhile back about the usefulness of an MBA. This oath would be a good starting point for defining the "value of an MBA." One of Josh's Blog contributors stated how abhorrent it is to have MBA's running projects. This is one of the typical nonsense statements made out of context and divorced of any domain.
As a holder of an MBA - not from Harvard, USC - go Trojans - I can say with unabashed enthusiasm, that going through an MBA program having started from a graduate degree in physics. Learning where your pay check comes from, how the place the pays you makes money, and all other financial, marketing, and accounting processes cause this money to appear.
As a project manager, this knowledge is critical to a project's success. Possessing this knowledge allows the PM to be directly connected with business and the business case for the project - at least in the commercial world.