Hmm, after thinking about it, here's an issue... At work, I am given a conceptual drawing to work from. Would you guys prefer to make your own concept, or would it be more interesting for me (or another mod) to provide a concept image and see what kind of take everyone has of it.
The main concern would, of course, be that everyone would be doing the same project, so stealing of ideas might be a problem... hmmm... and similarities would be pretty common, it being the same image. I suppose one thing we could do is find 3 or 4 different concept images and let people pick one. That way there could be some kind of variety in the challengers. Also, we could make a rule that any "he stole my texture!" remarks would be based on the date of the posts involved, with the copiers asked to stop. The concern isn't so much that people have similar work, it's the concern that someone posts their texture map, for example, and someone else decides to just take it and modify it (or even just blatantly USE it. :p ).