I definitely agree with the two above posters. It's based on the situation. I have a problem with your use of the word "promiscuous" though. The word has negative connotations. I love seeing pictures or videos of natural girls (i. e. not porn stars or models) who are naturally exhibitionistic. For example,
these pictures. Both of those pics are of wonderfully naturally exhibitionistic girls, which I would rather see over any shy girl in a bikini or underwear any day.
On the other hand, we have cases like
this picture, a situation in which a girl has something to be embarrassed about (especially since well over 10,000 people on this forum alone have seen her in all her humiliated glory). I think what it boils down to when it comes to ENF for me is that the girl has to be in an embarrassing situation, not just embarrassed because she's in a bikini at the beach or even in her underwear in her room. Now, if she's in a bikini or in her underwear in front of a group of otherwise clothed people, that's a different story.
Oh, and to add to Mad Scottsman's list, I would much rather see the "good girl" be embarrassed than the "bad girl" any day. The "bad girl" being humiliated is such a cliche that it bores me.
Fango