As previously noted, the Apple adapter from the new Mini DisplayPort to dual-link DVI (whew, long name) is a ninety nine dollar POS. Here’s some pictures of the failure mode, curable only via unplugging or sleep/wake:

This is unacceptable. Even when its working, now and then the screen flickers, so I’d guess they have a clocking problem. C’mon, Apple! Fix this damn thing.