On the one hand, it seems like cheating, what with letting the computer handle the perspective and reflections and shadows and such. Where is the craftsmanship? On the other hand, I have seen some spectacular works, and I, being an old pencil-sketcher, am probably mostly just jealous of the ability to experiment so freely with the ability to return to any arbitrary previous point in the creation. In the physical world, you can't undo that "oops" brushstroke.