Indeed. I live in a house with a few other people, and we make music a lot. I'll play the drums for a bit, and guitar for a bit, and when we're done I can generally be much more productive coding than I would have been if I had just sat down to code.

This seems to be from being physically active for a bit, and from having the creative juices flowing for a bit as well.

Totally. I can't tell you how much running for 40 minutes a day on an elliptical has changed my life.

Just bought a bike trainer (it stops the bike moving and applies friction to the rear wheel) and I'm doing 2 x 15 minute sessions per day. I'm about to get a rower so I plan to do the same amount on that, hence 1hr per day total. With just 15 minutes per day though (my easy-to-do starting point) it's made a tremendous difference to how I feel. Not sure I'm working any harder though *8) I just feel better.