I didn't have time to read through the entire thread (at work on lunch break right now), so my response is to the OP:
I remember reading that Myers (or maybe her mother) already had her own personality typing system before she came across Jung's. When she read Jung's Psychological Types, she apparently found that it was so similar to her own system and yet so much more superior/complete that she discarded her own partially-completed book and decided to adopt Jung's.
Well, I have a copy of Jung's Psychological Types and have tried reading it. I found the writing very difficult to decipher, but whatever I did get out of it I found quite different from the Myers-Briggs system. Jung always emphasized the dominant function and its opposition to the unconscious, "inferior" function.
Jung doesn't seem to say much about the attitude of the auxiliary function (whether it is same or opposite to the dominant), but I almost got the sense that he sees the auxiliary as being in a similar attitude as the dominant. So in the case of an Introverted Thinking type, the auxiliary would also be introverted though maybe not as distinctly introverted as the dominant thinking function.
Because Jung talks so much about the opposition between conscious and unconscious functions and attitudes, the portraits that he draws of each type shows more psychological complexity. For example, I remember very well the chapter he writes about the Introverted Feeling type. According to MBTI, Fi types are friendly, altruistic, and mostly harmless, angelic people who are quite incapable of being "bad". All light and no darkness. But Jung's Fi type can act out unconscious ("inferior") Te and become cold, suspicious, despotic, scheming and vengeful. He says that many women in history who have been notorious for their mishievious intrigues and ruthless ambitions are often examples of this type. Lady MacBeth?
Also, Jung makes a clear distinction between the perceiving functions and the judging functions. All of his perceiving functions (Ne, Ni, Se, Si) behave like Myers's P types and all his judging functions (Te, Ti, Fe, Fi) behave like Myers's J types. When I read Jung's description of the Introverted Intuitive type, for example, I can't help seeing how similar it is to the MBTI descriptions of INFP and INTP.
My opinion is that MBTI and Jung's system is not the same.
Edit: But I do think they are similar.