Perfumes and smells play a subtle role in human relationships, much less evident than in animals since we lost most of our olfactory capacities during our evolution from hunters-gatherers, when it was something much more essential for survival, but still there nonetheless.
Smell is the
oldest of our senses, the
least rational, and the
most relativistic.
A smell is a
chemical message, analogous to what simple, monocellular organisms use to exchange information and sense their environment. IIRC, olfactory messages are sent to the oldest part of our brain, the Reptilian Complex (
http://en.wikipedia.org/wiki/Reptilian_brain).
This would also account for its
irrationality: while we can recreate mentally a visual image or a sound, we cannot really recreate a smell at will.
By
relativistic I actually mean
time travel 
: you sense a long-forgotten smell, say of freshly-mown hay, and you are instantly catapulted back to when you were visiting your country relatives as a city boy, for instance.
Places have their own distinct smells, too: whenever I catch a whiff of rose-based air sweeteners, I'm suddenly back in a London department store or cinema. A certain type of sandalwood-scented Indian soap carries me to the Maldive Islands, where it was a staple bathroom fixture, etc.
And my favourite ladies' perfume is still
Eau de Rochas, fresh but with a subtle hint of lily-of-the-valley.
What's yours

?