As you say, wwh, there is more to this olfactory business than meets the eye.

Extract from "Sex and the Brain, Vive la difference!" report in today's New York Times:

"Several years ago, Swiss scientists discovered that women could sniff out genetic differences in potential mates. When women were asked to smell T-shirts that different men had worn, they often ranked more favorably the shirts that belonged to men with dissimilar genes for major histocompatibility complex, a group of proteins involved in immunity to disease. The odors a woman preferred also tended to remind her of past and current partners.

Seeking out different immune-system genes might be a way to prevent inbreeding or to arm offspring with a more versatile immune system, said Dr. Rachel S. Herz, a psychologist at Brown who in a study in 2002 found that women ranked body odor above almost every other factor in attraction, except "pleasantness."

Full story:
http://www.nytimes.com/2004/03/16/health/16SEX.html?pagewanted=2&8hpib