I took a little questionnaire in my high school English class in my senior year.
It wasn't a real one, but it was one of those where you had a box of I and E preferences and so forth (single box for S, N, T, F, J, P preferences, too, of course), where I had to check the box to see which one describes me better based on the set of words in each box -- it was like the thing in Do What You Are. I think I was INTJ then, too.
I stumbled across it again when I took the Career Personality Test at Tickle.com, again I scored INTJ the first time, but sometimes I come out INTP.
But then one day I came across David Keirsey's description of the INFP and found that I totally identified with what he said (that INFP children have very active fantasy lives), but not totally with his description of the INTJ or INTP. And so began my quest of self-knowledge...
I'm normally interested in one thing at a time and research it obsessively, then I'll go to another interest which I will passionately pursue for a while.
The way I pursue my interests is like a circle, I follow a roundabout path of interests but go back to what I was interested in at the start, and then I'll go around the circle again, and so forth. Of course, when I develop a brand new interest, the circle becomes more like a Spirograph doodle, where the circle deviates from the original path but will eventually come back to the original.