I talk to everyone. Of course, I think it makes a difference where you are. I live in a small town in rural Iowa. Even though I don't know anyone here yet, I talk to everyone I meet, and they almost always say something back.
I do. I used to work in retail and I think alot of it is by habit. The older and disabled people, I always try to. I have a disabled son and it really makes his day if someone just makes a point to say "hi".
Occasionally, but this would not be practical during the busy hours of the day when so many strangers are walking past.
If I pass someone very early in the morning I usually feel compelled to say Good Morning as a matter of courtesy.