One of my best and closest friends is actually an ISTJ, at least, I think he is one. I've never actually had him take the test - I'm fairly confident he would score as one though.
Our relationship actually started because of me, I approached him. I don't know if this is true for all ISFJs, but I'm a huge sucker for a person with a problem. I want to help them, and get them back on their feet. He was in limbo about this girl he'd spent the better part of his mature life with - she was a complete psycho, but he felt compelled to take care of her, like it was his job. In any case, it was something he didn't really want to do, but he felt he had a responsibility to do. It ended up with him not sleeping well, and drinking. I talked him down from this behavior, and reached out to him and eventually got him to trust me. He still has HUGE issues with opening up to me about his feelings, mostly because I think he doesn't register that he has them until they're boiling over. Most of the time when we talk, it's me talking about myself and my days, etc. Our relationship has actually taken a loss in that respect - to get to the point I was trying to make, we like to be trusted, and confided in. It sounds weird I think, but I liked that he was vulnerable because I felt it was a way that we could relate to each other. I like feeling that my companions and I can work together to solve our problems and make each other's hurts go away.