Laura Scott posted her 9 best practices and things to avoid when it comes to e-mail. We followed some of these rules a decade ago, but a good reminder is always appreciated. Laura doesn't mention anything about not using all CAPS in an e-mail and I assume that's because if you don't know that rule by now...nine rules is beyond your grasp.
My favorite rule to follow is number 3:
Write your response above the quoted text.