I've used many times in Asia. Usually, they'll quote me some crazy rack rate, but I've only paid it once. What ends up happening is that a cancellation occurs and my reservation gets (apparently) automatically "downgraded" from the premium rate to more reasonable rates. My guess is that if I hadn't used the privilege, I wouldn't be able to "slide into" the hotel at all.

Also, a number of times I've been able to make reservations at the corporate rate when other colleagues of mine (non-Diamond) have been turned away, even after having our local travel coordinator (who deals with corporate rate setting and minimum nights policies) call the reservations manager directly.