It is a very good tutorial, but it is maybe not for beginners. Some of the shader concepts were a little vague, and the measurements used didn't seem to match my Carrara settings (world is in inches, terrain is in miles, elevation is in thousands of feet..., and I'm not even sure where all those preferences are set). It did give me my first realistic-looking image with the new terrain modeller. Concepts like "add more bump for realism", and a comment mentioned outside the tutorial "darker skies mean you are at a higher elevation" are invaluable! Endless experimenting might not reveal those little tips. Thanks Johannes!