My two cents
I just have to say, as a former Psychology major, this thread is entirely too fascinating!
Here is what mine came out to today:
Ta-dah, your personality type is ISTJ!
Introverted (I) 89%
Extraverted (E) 11%
Sensing (S) 50%
Intuitive (N) 50%
Thinking (T) 85%
Feeling (F) 15%
Judging (J) 64%
Perceiving (P) 36%
Years ago I took this type of test as part of a retreat in my youth group - Conservative Baptist upbringing - and I was actually INFP then.
Then, when I first got divorced, I was in a workshop hosted by a Presbyterian Church in our town, and I came out ESTJ.
Now I tend to vary somewhat, depending on the day, my mood, the status of my meds - did I mention I am also bi-polar?

(My psychiatrist says I am hypo-manic.)
I have discussed this at length with my psychologist (I have the PsyD for talk therapy and the MD for the meds), and he says that the E and I interchange is actually common in some people. Some people can adapt very well to being extroverted in many situations, but then are introverted to recharge their batteries. I find that I am a lot like my parents on this - we all are very social when out and about or when at work, but when we get back home, to our "retreat", we need to wind down and not have outside distractions. My BF doesn't quite understand it - he doesn't understand why I don't like having people over to the house. My home is my own private area where I need to keep my introverted self separated from my extroverted self and the rest of the world.
As for poly, as I used to test INFP, I don't know if maybe that had something to do with my formative years, and perhaps I have always been poly (I am working this out in a very long fashion in my life story blog). Or perhaps now from the ISTJ perspective, as I thoroughly enjoy learning and researching and studying and analyzing, I simply have found a terminology and subject and group of supportive people who make sense to me, and who explain the way I have felt my whole life in a way that works for me.
I just know that, after discovering the word Polyamory in 2007, and devouring information on the topic since then, it makes more sense to me than the way I was living my life before. Though I admire, and crave, morals and values and structure, I also am always the first to question authority or the status quo, so perhaps a part of my personality says to society at large - why? Why does it have to be this way? Who says? Where does it say? What law is it breaking?
I heard a great line on a show once - not sure if it was a sporting event or a general TV show - "Rules are like the gates in slalom skiing: you get as close to them as possible without breaking them." That can be so true! While I respect rules, or laws, or even traditions, I still see the value in bending or challenging them - because in reality they serve a better purpose as a guideline rather than a set in stone mantra. The attraction to non-monogamy often times comes from a seeking out of something that non-conformists find can conform to their way of life, and not necessarily the other way around.
>^^<