I often hear programmers complain about being interrupted by people, breaking their concentration. Strangely enough I rarely have that issue. Every time people interrupt me my current context doesn't really get 'switched', rather I just do away with the interruption with the bare minimum of effort while keeping the context in my head. It takes a pretty big interruption to really disrupt my context, but as a consequence I probably seem a bit 'away' when responding to people while I'm trying to hold in the context. In some occasions when I've walked to the kitchen to get a drink, while concentrating on a difficult programming problem, I somehow lose the ability to have regular conversation, and I can only come up with standard replies to things. The same thing has happened to me in the elevator on the way out right after work, especially on days where I had to leave a problem unsolved. Oops. There's pros and cons to not being easily disruptable, I guess.