Another step by step example of how I sometimes use photoshop, and in particular the tool liquify, to clean up and improve my sketches. I wouldn't say all cheating is allowed, but in these cases I think it's a matter of making a sketch as good as possible rather than cheating. Underlay is another trick that I should probably use more often...

Equipment: Black Biq ballpoint pen

Time: 30 min sketch

Equipment: Photohsop CS5 (Liquify)

Time: 20 min