@Esoteric Wench's ISTP's comments were interesting to me and made sense on the basis of the probable ENFP friend I have. I think that for her everything is about emotion. She feels things in the moment with extreme intensity, to a greater extent than I do (certainly with more obvious intensity), but also seems to move on from or...reframe those emotions more easily (or just differently?) from me.
I think that with anyone it is best to keep a close eye on their actions and to not put such weight on their words; unless of course you find out over an extended period of time that their words are extremely reliable and consistent (and I do have friends like that - they tend to be fellow IxxJs, and my IxxJ family members are also pretty much like that so it's what I was used to growing up.)
With the above-mentioned friend, if I pay too much attention to what she says, or take it much too seriously as an indicator of how she's going to behave next, I'm going to feel let down or even (depending on the situation) betrayed. However, I've known her long enough to know what her patterns of behaviour and priorities ("core values") are like. I tend to pay more attention to those now and less to her words. (Admittedly, she has also had some pretty tough stuff happen in her life and that has made her more emotionally volatile and drawn to drama; I have to factor that in too and it is somewhat outside of type.)
It does seem to me though, and still annoys me, that she doesn't seem very self-aware. She's married now but in a somewhat tricky and frustrating situation (husband still lives in another country). She said to me the other day "you know, even when I was single, I was never really the type who was desperate to be in a relationship, obsessed with guys or 'needed a man.'" This not only contradicts stuff she's said herself ("I NEED to be in a relationship"), but very much contradicts her whole pattern of behaviour while I've known her and what she's told me about her past (falling for one guy after another, idealising men from a certain culture, getting married in a very precipitate manner after only knowing the guy a few months and only spending a few weeks actually in his company, etc.)
Of course this may not be all type-related. But it is interesting. I do think that people express their "core values" in different ways and INFJs may be more prone to actually stating them and giving a lot of thought and weight to words before saying them, while other types may show the "core values" more through emotion and action. I mean, this friend of mine, her words may have been inconsistent a lot of the time, but really her actions and her expression of emotion have been pretty consistent.
EDIT: I think ExxPs live in the moment in a way I don't really understand. So - and please correct me if you're ExxP/Fi user/etc and feel I'm wrong - I get the sense that even when they are talking about the future, they are viewing it purely in the terms that they are viewing the present. So when my friend lost someone very dear to her (he actually died) and she said she would never love again - she said this many times over the course of several months - this intensely reflected how she was feeling at the time, and understandably. But I think she was seeing the future purely in those in-the-moment terms too...not that much later, she'd found someone else. Rather to my shock (and my concern that she'd not properly moved on from the last guy - which I do still think is possible.)
For me, I think I am more future-oriented in terms of knowing that the future will be different... I know very much the feeling of being in the middle of a sad, painful situation and feeling like it will never end. But I still KNOW it will. Especially having been through experiences like that before and coming out the other side. It helps me get through, actually, even if the pain is neverending while in it. So, if someone breaks my heart, I know in the moment that the heartbroken feeling feels like forever; yet I also know that eventually it will wear off, at least enough for me to get on with my life, and that just possibly a day will even come when I slightly wonder what all the fuss was about. And I don't want to go out on a limb and look like an idiot (to myself anyway), so I won't say things like "I'm going to feel heartbroken forever and will never want another relationship", or "this was the love of my life and there will never be another like it." I may have feelings like that in the moment - sometimes for very long and painful "moments" - but I know that the feelings will pass on to a great extent, even if it takes what feels like forever.