I wonder if this can be applied to a startup, not just romance. The first few things that comes to mind are Apple's "just another day that you will never forget" and Google's Cr48 pilot program. Both have an element of uncertainty. In Apple's case it was the nature of the announcement, and in Google's case it is whether or not you will get one of the pilot laptops.

In both case people's attraction seems to have been peaked more than it otherwise would have. So uncertainty can be a powerful tool if used properly.

Of course, I'm thinking about applications towards startups because I'm not a really socially adept person, and am therefore not too sure how one could go about deliberately creating uncertainty in a social relationship to attract a female.