I've seen this - I was part of a large company that threatened to move everything, not to open source, but to google docs, and MS sales team moved heaven and earth to reverse the decision.
It's not just that they don't want to lose a customer - they don't want lots of examples out there of how it can be done.
It's not just that they don't want to lose a customer - they don't want lots of examples out there of how it can be done.