I do think I get an insight about someone when I am dancing with them (especially improvisational forms) that give me a strong impression about them as a person: how much they listen to their partner’s movements; how creative they are, etc, etc. which may be useful in gauging their sensitivity as a lover.
Furthermore, when I dance with someone (and not just looking, I mean, partnering with them) I think I get a sense of how they relate specifically to me.
In improv forms—just like in the bedroom—partners start developing their own kinaesthetic language; and so when I dance with them I can get a sense of how well the person “clicks” with me… which is nothing to do with how sexy they are in movement; but rather, the colour of our relationship.
Of course, people are very multidimensional, and what comes out in a dance may be a very different aspect to what comes out in bed. As seekingwolf suggests, there’s the public/private sphere. Certainly I’m happy to play in private in a way I wouldn’t do in public.. there’s a freedom there to express yourself in a different way.