I've been properly tested, and come out as INTJ. Interestingly enough, however, my introversion is slight based on my social "abilities", but strong based on my general character/preference. I often prefer writing music or reading something interesting to going out, but, once out, I can easily act like an extrovert (holding the centre of attention, speaking in front of many people, getting on well with new/unknown people). Most of that is simply learned behaviour.
Essentially, introversion is nothing less than an enabler, while extroversion is a "norm".