People that believe in God are the new black.
Collab Splits
It's hard to be fair when coders don't understand what goes into good art, and artists don't understand what goes into good code...and neither can be judged strictly by hours because often, the better you are in both fields, the less time it takes to make something awesome.
But, my experience has been that people are generally pretty fair when it comes down to deciding the split at the end of a project. Even though I haven't done the "decide at the end" thing on many projects, I agree that the end of the project is the best time to make that judgement, though sometimes knowing how much $ is coming your way early on can be motivating.