I know heaps of them (I think). At first I typed all of them as ISTJ, I showed one a description, and they were quite impressed by the accuracy. Then I started to realize a few differences between some, and determined that one of them was ISTP. I've now got somewhat of an idea of the difference. Both types are incredibly clever, I haven't seen one that isn't. As far as I can tell, ISTPs lean more towards aggression, mechanical work and tools, and intently dislike pointless knowledge. They prefer to deduce knowledge from logic. ISTJs are rather less aggressive, when they get into a car, they are less likely to try to do burnouts and crazy shit (ISTPs can be quite serious drivers when they choose to be though). ISTJs will pillage through mathematics using set concrete methods that they have memorized, if you get them to check your work, they will be the first ones to notice your mistake, an ISTP probably wouldn't bother checking your work, if they did, maybe they could find your error, but they are less 'picky' when it comes to detail. I could probably add a bit more, but I must sleep now