Observing lines of people awaiting their turns to be attended is always curious. See some examples below that shows various distance between the person using the vending machine and the next person in line:

Why do I blog this? "Proxemy", a topic I have often addressed here few years ago corresponds to the the physical distance we maintain during interpersonal interaction (see Edward Hall's writings). It can depend on cultural characteristics and contextual factors of course.

What is interesting is that this concept (and the aforementioned examples) can be applied to the design of mobile services (and of course the usage of mobile devices also influence proxemics in a certain cases).