Back in 1995 or 1996, I spent a long week-end doing extreme pair programming with Philip Nelson. We set up in his dining room and took an image from his whiteboard to a 80+% done product in 3 or 4 days. No meetings, no phone calls. With very few interruptions, we were able to maintain focus for hours.

The most notable interruption: while stretching, Phil accidently hit the rocker switch on the power strip with his foot. I'll never forget the look on his face when everything shut down. We only lost a couple minutes worth of edits, 'tho. I am a habitual save guy in emacs, whenever I switch buffers or pause to think.