INTP, by most versions of the test I've taken. I seem to come up 51/49 on the T-F axis, though.

Almost all my friends are introverts (all three of them--hee!), but there are a couple of notably extraverted exceptions with whom I share the drifty-brain, an enthusiastic pouncing on some new idea or interest, and the inevitable fade.

I don't have a strong theoretical grasp on the MBTI, but I wonder if the Calder-mobile-mind isn't generally a trait of Intuitives.