A while ago, I asked this question. The answers seemed to suggest that if the question is about emacs rather than about lisp coding or whatever, then it should go on superuser. So I had a question that I assumed was about emacs. So I asked it on SU, but within seconds it had been migrated to SO. Someone on SO voted to close the question.
So I think there needs to be a better policy on where these kinds of questions belong, and it needs to be consistently applied.