Commuting plus recreational riding is the majority of my exercise. I used to run on a treadmill while watching movies, but got shin splints on several occassions so I stopped doing that.

I enjoy walking, its not uncommon for me to go for a 12km, 2.5 hour walk to the store for a loaf of bread (when its warmer, ie: above -20C). Walking as exercsise is ok for weight maintenance, but don't count on losing weight doing it. One summer I walked about 15km or more (3+ hours) a day and didn't lose any weight at all. I can see how people can get frustrated, but you can't expect much from such a low intensity activity.

On long walks I find the front of my upper legs get stiff. Once when I went for a 30km, 6 hour walk I think I injured the facia on one leg. It wasn't painful, just a really unpleasant feeling that took a long time to heal. Now when I feel my legs tightening up I slow down and do some stretching.