A very good friend of mine is an ISTP. She is VERY straightforward and does not hesitate to say what is on her mind (to people she knows well, to strangers, she can come off as reserved). She's a ton of fun to be around with, and very sweet, though tactless at dealing with people at times. She excels at math and science, but is not a very good writer nor does she like to read. Very grounded in who she is.
I think ISTPs are great to vent/talk with because they help you get over "unnecessary" emotions.
However, as teachers, they can be rather detail-oriented, which can sometimes be unecessary and confusing.
Good at practical things, at times really obedient / make a good follower. *mwahahah >D* Pretty realistic at times.
However, they don't really see things beyond what existed, or had existed. So it's pretty useless to talk about concepts or possibilities with them. :| Also, very tactless, at times to the point of blatant ignorance. And only energetic at things they're into atm. Otherwise...lalalala~~