Fia's descriptions resonate with me and my experiences with an INFP boyfriend and several INFP close friends very well.
I also have found as time has gone on that while Fe/Fi may seem like a clear difference, Ni/Ne differences are actually probably even more profound and affect outlook and thought process considerably.
I might add that for me, my dom/tert loops (Ni-Ti) tend to be centred around organizing things in my life which don't seem to easily resolve themselves - whether behaviour of other people, or content of information I need to be responsible for and so on. It seems that when there is a strong emotional element involved that includes some contradictory information, I get stuck endlessly looking at things from different perspectives, structuring the information, and then feeling that I left out something important and having to start the whole process from scratch, leaving me stuck for a time and looking for some kind of Se escape like sleep, spending money, watching mindless TV, being overindulgent, etc.
On the other hand, INFP dom-tert loops (Fi/Ne) seem to be centred around their own internal beliefs/feelings about themselves (at least from an observer perspective) and both coping mechanism escape and the key to getting out of the loop are in different areas than with an INFJ, as the loop is centred around different issues.