People around you (especially non-engineers) coming over just to know whether you saw their instant message ping / email to send them a value of a configuration. Or others who just comes in at the right time - when you just got into your utopian magical zone - "just to say hi and catch up". There goes the rest of my day.

Complement that to the instant messaging application of choice of the organization and it's a no-no for productivity. I find myself being invited to random channels only because they want to mention that I did something. I set myself to Away whenever I'm in the mood, but that still doesn't stop people from pinging and sending me notifications anyway.