I actually think INFJ and ISFJ can be quite compatible. The attraction would be based more on having several similarities and thus mutual understanding rather than opposites attract kind of spontaneous chemistry. The similarities lie in both types having Fe as secondary and Ti as tertiary function. Both type of people will strive to look out for each other, to be nice to each other and please each other, but when threatened both can also become selfishly calculating. In this they can understand one another's view point, decisions, and support one another. The miscommunication comes from ISFJ having dominant introverted sensory function and INFJ having dominant intuitive function. When I try to talk to my ISFJ mother about something a bit more abstract for example I just don't find understanding in her. Occasionally she can kind of relate and add a bit, but conversation of this type with her just does not flow. However when I talk about concrete down to earth things then she can very easily relate, but I just feel bored and shallow talking about these subjects. Over time though I have grown a bit fascinated with how she sees the world, as I have always rejected seeing it this way, but practical reality cannot be ignored. Another point of contention is that I like and welcome change, while she seems to want get firmly rooted where she is and not change anything. Both of us can also be quite stubborn. However we also complement each other is some ways - I can provide like a strategy, a long-term plan of action that she would listen to, and she is very good at noticing details and also taking care of practical things that I'd be too lazy/bored/inattentive to take care of. She is also a much better homemaker than I will ever be.
You also might want to visit this forum:
Infjs Forums
I was browsing threads there and remember one INFJ guy posting that he is married to an ISFJ and he sounded content with the relationship.