My younger sister is an INTP. All in all, she is wonderful company, and is very opinionated and observant, witty and silly. She can be a little agitating at times, and even admitted that she likes "getting into arguments" (read as "debates" of a sort), but doesn't do it with people she doesn't know, so she saves that for me, haha. But it is only over opinions on stuff and never anything serious.
I am very glad to have her around, because she's helped me out emotionally many times. And the perfect soundboard for my ideas too, because she is very mature for her age (intellectually, but not always action-wise!!! She is REALLY odd at times) and has even more common sense than a lot of my acquaintances, lol!