It used to be a no-no because it was confusing. Agent Smith said at one time or another that he doesn't mind, and that he can keep track of it. I don't see a problem with it at all. I think it's especially fair to those who post early on because they can rework if they want. Renderosity and its forums are designed to be communities where people can discuss their work and use criticism to their advantage. It seems silly and contrary to the very tenet of the forum to disallow this for a challenge. The only thing I think that would be unfair is if people are using old images for the challenge. I remember reading that one of the rules is that the image must be new (to keep us creative), and that makes a lot sense to me. Basically, as long as the guy who has to moderate the challenge (AgentSmith) can keep up with it, I think it'll continue. But it's probably only a matter of time before a vote goes up with someone's first or second draft. Perhaps posting a pic as a rough draft and not as an entry would be a less confusing solution, but again, I suppose that's in the hands of AgentSmith.