For what it is worth, I do think Dustin could have been a little more gracious in how he approached it and I mention in my note that it isn't meant to be an excuse to be rude. I actually think it was fine for him to do this to me not because he was my boss but because we had a good relationship. Still, when this happens to me, I usually say something like "I'm in the middle of X right now, can this wait until Y?" -- this tells them what I am doing (and thus allows them to say assert that their topic really is more important) and also gives them a time to follow up.

As a manager of a large organization, I have more respect for people on my team who say no and assert stronger ownership over their time, ideally by being transparent about their priorities. At the end of the day, we just look at impact and managing ones own time is a good sign that someone is focused on impact. Still, I'm sure that isn't the case with every manager in every company (or even every manager in my company)

The open space aspect of the FB offices is usually navigated by people putting headphones on to indicate they are heads down. I do it often even though I'm rarely listening to anything. I agree it isn't for everyone though.