I am amazed more people haven't found cycling as a form of exercise. It is a total revelation for me - 4/5 months ago I could barely get to the local shops & am now comfortably cycling 20+miles and LOVING IT! I've never really enjoyed exercise or found a sport I was any good at (used to force myself into the gym or to classes to keep trim) but I actually look forward to going on my rides. Oh and my legs have never been firmer which is always a bonus 
Is it because, like me, people assume they just can't ride, or fear of traffic etc?