I'm basically paid to be on-hand 9-5, so that's what I do. I don't check email outside work hours as a rule. If there's something technically interesting, or is important to do but cannot be done within the constraints of a business workday (basically, anything that involves deep thought, concentration, and sustained effort), I may choose to do it when that's convenient for me. And I know things; I remember, and I've been around long enough to know the whys and wherefores and sequences of events that led up to the present state of things.