lots of those groupings are useful, but i probably make the biggest distinction between NP, NJ, SP, and SJ.
also, @ everyone who is calling IJ the doer....i don't think that's quite accurate. i'd call IJ the data-collector or something like that. the doer is more like EJ.
(i'm definitely not a doer.)
IJ: the data collector/observer
IP: the thinker
EJ: the doer
EP: the explorer