Can you extrude along normals as opposed to an axis?

 From:  WarrenM
If I subtract a cylinder from a cube and select the rounded face it creates, is there a way to extrude that face along it's normal or does it HAVE to be axis locked? I'm finding that non-intuitive as I play around. It'll extrude flat faces along their normals but not curved stuff. Or, can I define the extrude axis ahead of time somehow with a guide line?

EDIT : Aaaaand now I see the "Set Dir" button in the Extrude tool. Never mind! :P