There are many different preferences for distance between two people in any given culture. There are intimate, personal, social, and public distances to be aware of. Many can be similar, but the ones that are different have the likelihood to cause discomfort or confusion for one or both of the people in the situation.
In America, our cultural norm for social distance is four to twelve feet! Then, for the Saudi Arabians, their ideal distance for conversation is only nine to ten inches.
This difference in distance could cause a problem, such short distance has a great chance of making any person uncomfortable. Say someone starts talking, just friendly conversation, but even a stranger that wasn't known and they came that close to me I would back up quite a bit. It's just an awkward situation most people would not like being in. Each person has a comfort zone, it is important that space needed is given. Invasion of this comfort zone probably has people freaking out a bit inside when it happens, but to be polite most will just try to step back and continue conversation. Well, untill they can leave, then say they're glad that's over.
It all depends on who you are talking to, if it's a close friend or a person your in a relationship with, your bubble won't be very large because you are both comfortable with eachother.
http://en.wikipedia.org/wiki/Personal_space