YOU JUST BROKE MY FLOW AND STOLE 2 GOD DAMNED MINUTES!
Actually, it's worse than that. The (average) time it takes to get back into flow is 15 minutes[1], so add the time to respond to them to that to get your wasted time. And if you get another interruption before the fifteen minute descent into flow is complete? Start over - another fifteen minutes. If this happens constantly, you will effectively never get any work done. There's more than one way to kill productivity.
Actually, it's worse than that. The (average) time it takes to get back into flow is 15 minutes[1], so add the time to respond to them to that to get your wasted time. And if you get another interruption before the fifteen minute descent into flow is complete? Start over - another fifteen minutes. If this happens constantly, you will effectively never get any work done. There's more than one way to kill productivity.
[1] - See "Peopleware", Chapter 10.