I believe that commuting on a bicycle is easy to do, and almost anyone can do it. I also think getting regular exercise gives a person more energy and focus, not less.

To answer the original question, I depend on my bike to get to work because I don't own a car and there is no public transportation to my workplace. Even if there were public transportation, I'd probably bike anyway. I live in MA, and riding in New England snow and cold is quite doable, and enjoyable. My commute is 17 miles (34 R/T) and takes me about 1 hour 20 minutes, and I love it! it is the best part(s) of my day frankly. I don't get sick often-- knock on wood-- but maybe that's because I get regular exercise from riding to work. Actually, if I am not feeling well, going outside and getting on my bike actually seems to help.

My favorite part of the day is early morning before anyone else is on the road, save for another bicycle commuter I sometimes see when I'm about halfway to work.