I think this depends mainly on the age of the two. I'd theorise that the older the couple, the further away the relationship is directed away from hitting rocks. This is of course a flawed assumption, but it does hold some logic.
I'm seeing an ISFJ. We're both young - I'm 18, she's 18 at the end of May. We're both still developing in terms of maturity at different rates, and in different ways. For instance, my Ti is almost fully developed, whilst hers is barely in the embryonic stage; this applies to her Fe being developed, and so on. At this point in time, we couldn't be on more different wave lengths. For one, she likes films, and music, and getting involved with peoples' lives; I... don't. What doesn't help is the distance (I live 2 hours away) and the fact that our relationship is clandestine (teen dramaz alert) so in fairness, I think our relationship in particular is more likely to sink than any other ISFJ/INTP adolescent couple. Not that I'm a pessimist or anything, I'm just being realistic (unlike her).
But anyway, yeah. Our mentalities are completely different, but I find that is what makes her so compelling. It's impossible to rationalize. I'm guessing my ISFJ found herself drawn to my social eccentricities, or something. The sceptic in me doubts she wants personal growth out of the relationship, so perhaps she sees me as this clod of putty to mold later on. I, for one, sought personal development out of it (as well as finding her attractive) because yeah, I found that listening to input from her perspective helpful; she helped prevent me from becoming stuck in a rut.
We do have a similar sense of humour, which from my perspective is the cement of the relationship. But we still operate on different wave lengths and there is the inevitable risk of miscommunication, "Wait, what do you mean? :?" which I find a little disheartening. Plus, being introverts, we both have the tendency to showing reluctance in expressing our emotions towards one another. We both expect the other to initiate, so I find myself having to volunteer myself, which goes against my nature. Then again, I gain something by it by developing my Fe; I initiate my affections, she shows her appreciation, and thus I learn to express myself more.
We have our problems, but they'll either smooth out with time, or they'll be the end of us. Only one way of finding out. *shrug*