I definately understand what you mean about the marble/clay comparison. Being a young writer, I've trashed more stories because I couldn't get the words to come out right than I can count (okay, I could count them, but I haven't kept track). Of course, being a beginning writer, they really weren't very good to start with. I'm actually working on something that is actually half way decent right now, or more acurately fighting with writer's block over something right now. I really like your idea of a dump file, I may have to try that, instead of deleting the sentence and then wanting it back, or keeping a not quite right sentence in.
~ Corinne