Jeff Schoolcraft has an interesting post on Pair Programming and how it influences your break schedule. Two people working together certainly helps to avoid distraction and remain "on task" (asides from all the other benefits) but is it unhealthy? Should there be a "pairing-o-meter" which turns red at some point and causes the pair to stretch their legs before the dreaded window incident Jeff alludes to? :-)
At our current client, there is an outside balcony which allows us to look over the downtown and get a breath of fresh air.