As a Language/ESOL major, I have learned that one major component of language is knowing the appropriateness of usage and context. People adjust their language usage and patterns according to context and their audience. It's fascinating to analyze, really, (but I'll let you take my word for it).
In a way, MBTI bugs me because it tries to box each of us in to nice little personality boxes that attempt to account for our behavior and decision-making processes...when really, I am a personality code-switcher. Not to say that I have multiple personalities or am suffering from schizophrenia or something, but really, I adjust my behavior and the personality that I portray based on the context and skills that a particular situation calls for.
For instance, when I am at my restaurant job, most people would probably think I was extroverted. I force myself into small talk with people -- I put on a show. I smile, I make jokes, I play the charismatic card fairly well.
When I'm sitting in my classes, I am quiet, reserved, and I only speak if I feel I have something of value to say.
When I am tutoring students or teaching a class, I'm speaking clearly and with confidence. I usually remain casual and collected, but I always try to be prepared and organized even though a lot of times teaching calls for spontaneous, off-the-cuff clarification and examples.
When I'm at home, my room/house is often a wreck. I have a pathway where I can walk to the bathroom and to the blinds so I can open them. My stuff is everywhere. I prefer it organized, but I figure I'm meticulous about everything else, so I can stand to let this part of my life go for a little while until I have time to address it.
When I'm with friends, I can be either the quiet one, the mean/sarcastic one, the nice one, the go-getter, or the laid back one -- all depending on which friend I am around.
When I think about it, identity, in a large part, seems to be shaped by the relations we have with people and the way others perceive us. I am the same person, and yet I play many roles according to what skills are needed and the people who are around me. I don't change my value system, but I do regulate my behavior. So what "personality type" am I? I don't really know.
Is my personality who I am when no one else is around?
Is it the role I am most comfortable playing?
Is it a reflection of my general tendencies across all situations?
Blah, you know what? I'm a believer that everyone chooses for themselves who they want to be. Sure, we have tendencies and perhaps biologic impulses toward certain behavior, but when it boils down to it, I choose who I will be.