From James Fallows:
Allen's "two minute rule": if a task comes up that you think you're ever going to do (write a thank-you note, look up a reference, make a call), and if doing it will take less than two minutes, then you should always do it now. The rationale is that keeping track of it to do it later would take much more time than those initial two minutes, and delaying it will cause you mental friction in the meantime. If it's more than a two-minute task, then it's worth treating it as part of a longer-term system (which Allen also lays out) for keeping track of what to do when.
The sheer amount of time I spend feeling guilt about e-mails I haven't returned is astonishing.
