Here’s the problem. Snow Leopard is seeing the Cintiq’s default refresh rate higher than its native 60hz. Using a third party app named SwitchResX, I created a custom 1650×1080@60hz resolution. I rebooted my MacPro, applied the resolution setting in the Display SysPref PrefPane, and, voila, no more problem.

An official fix would be nice, though. Hear me, Apple & Wacom! Old man Frenden shakes his fist at you with scorn and malice!