Rick,
No marks as of now but for the future I cannot say, I think with careful handling when putting it down on the cooler there should not be any more risk that with the other metal coolers that are available.
It is important to specify which model it is for, as there are recesses for the feet to sit into and the large recess position cut into the base may be different model to model.
Hardware Monitor and Core Duotemp seem to agree that after a hour the temperature sits around 48 degrees. Being new to the Mac system I really do not know if that is satisfactory, I would just add I have never seen the claimed 28 degrees as shown in the Youtube video (only on the way past ! ) but the case does feel cooler to the touch, I was concerned about the temperature when I first had this machine as the base of the case along the edge where the screen hinges was almost too warm to touch.
Mac Book Pro Mac OS X (10.4.8) Photography, motoring, European travel