I've got the 27" display right from right before they switched to thunderbolt. Same issue. The machine will wake but the display doesn't come on. Then it will go back to sleep.

I'm using BT Apple keyboard and trackpad with it. What I do in this situation is plug and unplug a USB device to try and force the machine to wake. It works most of the time after 1 or 2 plug/unplugs.

But sometimes it happens just with the built-in display. For instance, I'll sleep the machine and then unplug it from its Henge dock which removes all external devices at one time. For my typical setup that's the display, the display's USB cable and a USB audio device (which isn't being used) plugged into the display. When I then open the system up I'll be greeted with a black screen. Every once in a while I can close it and put it to sleep again, then open it and have it work. Most of the time when this happens I have to force-restart it to get the display back.

When I worked for ATI, always on Apple contracts, if this happened 1 time in 3000 attempts, it was a block ship. Period. We'd be there working 12-16 hour days through the weekend until it was found and fixed.