i am an infj and my mother is an estj. while i can't help with what romantic relationships between the two are like, i can tell you that the relationship we had as mother and daughter was VERY rocky for a while (probably from about my age 13-19). i am not sure if this is because of developmental milestones and our differences (Fe developing and whatnot, as they say certain functions do at certain periods in your life) or just because of the fact that we were so different (most of the time the rockiness was due to my being very upset that she wouldn't let me be myself and my feeling that she did not care enough about me--the deep inner me). i think the weakness, then, is that estjs can be very point-a-to-point-b without much room for wavering and also that they strongly desire to take control of everything (which strongly smashes against infj--or any nf--need for independence). also, she overwhelmed me with her STRONG extroversion (detail-oriented, thinking-focused extroversion, which felt really cold and draining). probably for her, i was frustrating because i was not detail oriented (which she thought was downright rebellion at times, but it wasn't--i was actually a VERY conscientious and focused kid) and also because i was not willing to accept being told something "just because i said so" if i didn't believe in it myself--i had too strongly deep-rooted convictions and free-thinking thought.
however, as i grew older (and moved out--that was probably the biggest thing), our relationship has actually grown to be a pretty good one. we do understand each other pretty well now and can enjoy some good, even relatively deep conversations at times. we also have fun when we go places together. all of the things that are listed as benefits of a "duality pair" on socionics.com (which actually has a lot of good and very true--at least in my opinion--relationship descriptions of the interactions between different types), as another poster provided the link for. i think the relationship between infj and estj has the potential to be a very good one, but if it were one where they were going to be spending a lot of time together and/or, especially, living together, they would have to be very open to working toward better understanding one another and each other's needs.