Prompted by Miss Magnum's post:
In a recent US News & World Report (maybe a handful of issues back), there was an article of a study done by some university, on preferred scent / attraction to mate.
They took 80 freshly sweated t-shirts, and had subjects rate them for attraction to smell. What the study concluded was that, we more prefer the scent of someone who has, a more different immunology mix, than our own mix. Restating, we're not too interested in someone who has similar immunological fingerprint, and seek the "complement" to our own.
Article also said, that most of these immunological components, aren't conciously detectable.
Have heard women mention how a man smells, fresh out of a shower, after exercise. Plain Ivory soap, after an afternoon of gunpowder, seems to be okay.