I think there are a lot of factors that go into this. Moderation is definatley the key. It is often fish specific as well. For example, many tangs will graze on the various algeas in your tank and could probably go several days if not longer without an external food source, where as other more delicate fish require food sources that may not be found naturally in your tank. In a well established tank with common fish, I think it's safer to err on the side of caution and under feed, because a larger (say 55 gal +) tank that is well established will have a significant amount of naturally occuring foods for many types of fish. JMO
Oh, I generally feed a small pinch of flake and cyclopeze daily or every other day if I forget. (yellow tang, violet psuedochromis, domino damsel, false perc., lawnmower blenny in a 75gal).