Enough said about productivity, from 37 Signals.

We all know that knowledge workers work best by getting into “flow”, also known as being “in the zone”, where they are fully concentrated on their work and fully tuned out of their environment. They lose track of time and produce great stuff through absolute concentration…trouble is that it’s so easy to get knocked out of the zone. Noise, phone calls, going out for lunch, having to drive 5 minutes to Starbucks for coffee, and interruptions by coworkers – especially interruptions by coworkers – all knock you out of the zone. If you take a 1 minute interruption by a coworker asking you a question, and this knocks out your concentration enough that it takes you half an hour to get productive again, your overall productivity is in serious trouble.

Joel Spolsky