Another variable affecting sleep quality? How about exercise and physical activity?

How many of those that are sleep impaired are on the couch or sitting most of their waking hours? I generally sleep 8 + hours a night and am asleep within 10 mins of hitting the pillow. I follow Carl's three rules but also am physically active here on my mini-farm and exercise somewhat regularly.

A good day of physical activity and I have no problems getting a good night's sleep.