OK, I think there are actually many differences - obvious, as planning stuff, liking/disliking decision making etc, but I want to write about the two 'easiest to spot' differences:
1. Privacy
ENFJs will tell you a lot of personal details, but to the point only. Nothing about family problems or so (if he/she does, you're a super close person).
ENFPs on the other hand are much more open.
2. How they move and look.
ENFPs are often charmingly-clumsy (my good ENFP friend is dangerous to be around when having a cup of coffee in her hand

). Also their fashion style is.. very NF. They also move around a lot.
ENFJs look more socially-acceptable, but often with one little personal, extravagant detail. I didn't notice ENFJs clumsiness, though I get a bit tensed when somebody watches closely what I do. We're also really relaxed among friends (I am constantly told I sit like I own the place

).
So, the two.
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On the other hand, a very intriguing difference for me is the morality these two types present. I'm pretty sure some ENFJs will not agree, but I'll write it anyway, because I'm intrigued if you also feel this way:
ENFPs have their own moral code. Pretty crazy sometimes, but very stiff. It often has nothing to do with the one society follows, but still THEY HAVE IT. Must be the Fi, I presume.
ENFJs are more.. hm.. conventional. The morality steams more from empathy. We also have this 'save the world' thing...
Damn, am I selling our secrets??
Cool thread, btw.