When you walk, do you think?

When you walk, do you think of anything? I always think of something when I am walking. I believe if I do so, I do not waste my time. I think I have this habit because I have to commute everyday. I see people listening to mp3, reading newspapers, talking on the cell phone, playing PSP or NDS, checking their email from Blackberry etc, and it seems they enjoy what they are having in their hands. The only ramification of doing such things on the MTR would be missing getting off stations. However, it is totally enjoyable.