If you want to use an exclamation mark aswell as a question mark, is that OK, or should you LEAVE OUT the question mark? eg."The spell worked - and WHO said he doesn't believe in magic?!"
That's a personal opinion only, so feel free to gather some more...
I would prefer not to use them together, especially in more formal texts. Depending on the situation, choose either the question mark or the exclamation mark.
Naturally, in informal texts (i.e. emails to your friends) anything is permissable, isn't it?!?!?!?!?!?!?!?!?!?