USE OVERLAY IN THE CLONE SOURCE PANEL
Have you ever used the Clone Stamp tool and wondered what exactly you were going to paint in the area? Wonder no more. Now you can turn on the Show Overlay checkbox at the bottom of the Clone Source panel to automatically see an overlay of the image, as you would clone it. Also, by default the "Clipped" option is turned on in CS5 and that clips your overlay to the actual brush size. If you want a full image overlay (which you probably won't because it's really hard to see your original image) you can turn Clipped off. One more thing. You can automatically turn this feature off and on by turning on the Auto Hide checkbox.