I just ran across this article in the Economist about why we pick the scents or perfumes that we do. Three basic messages there: first, scent makes a guy ACT differently, in a way that is apparently more attractive to women--so it's the way he acts, not really the scent, that gets the girl. Second, we pick each other based on scent, and we look for people whose scents are different than our own. Third, DO NOT BUY your significant other a new scent unless you aren't getting along.
This makes me remember this research, though: birth control pills alter women's sense of smell. So if your best girl is on the Pill, go ahead and buy her the perfume. But if she quits taking them, she'll quit liking it and you!
And this seems like a questionable idea. Really, I can't think of too many women, Pill or no, who would go for this.