To a co-worker: you left me a voice-mail message with an urgent request when I was gone for the day. When I returned, I worked it first thing in the a.m. and then sent you an email explaining status, upon which you replied, "don't worry, I figured it out and got it done while you were gone."

Thanks - that's 20 minutes that I wouldn't have wasted if you'd sent me a 10-second follow-up message. Simple etiquette, people !!