This has been plaguing me for a while since I updated to Mac OS 10.8. Dragging layers in the layers palette of Photoshop CS4 would cause an immediate crash to desktop. Finally found a solution in this thread which worked.
Solution: turn off the OS power-saving graphics switching.
It's the checkbox at the top of the Energy Saving preference pane:
You'll need to ensure that it's unchecked and probably restart after that.
Now I can drag layers all day long.