...So as I was saying, he makes good points but he also invokes math. Whenever someone on a blog invokes math to make a point about computer programming, it is healthy to be a tad skeptical. (Even if it's Steve Yegge. Even if it's Paul Graham.... hell, especially if it's Paul Graham.) In that spirit, here is some nitpicking about Ethan's assumptions.
If they don't interrupt you now, then the question they need answered doesn't get addressed in a timely manner. That might also mean lost productivity.
If you aren't on break, you are in "the Zone" — all the time? Are you really in the Zone 6 hours a day? Aren't you ever compiling?
If you are interrupted for N minutes, Ethan assumes it takes exactly N minutes to get back in, regardless of N. That's seems arbitrary.
When you are spending the N minutes getting back into the Zone, is that all pure waste? I would imagine it's just normal work with a bit less momentum.
Still, it is something to think about. Cheers!
P.S. And by "something to think about" I mean to say that Ethan's conclusion is more or less correct. It is only his reasoning that is a bit flawed. There's no doubt that interruptions do waste valuable time. I also think the best reason to avoid interrupting people is they don't like it. Particularly not Ethan (or Dan). However, "Borrowing at 100% interest" is a much more compelling title than "Hey, that's kind of annoying!"