While I am not scent-sensitive, I have several friends who are. People wearing too much perfume can actually cause them health problems. I've seen friends have to leave restaurants or have to move seats at movies due to someone who is a walking chemical cloud. My own personal dislike is guys on airplanes who seem to be drenched in nasty cologne that burns your eyes.
While I don't often wear scent, I would not be personally offended if someone told me my perfume was too strong to them because I know it's not something the people with issues do casually and that they often feel bad for having to say so. That said, I purposely avoid perfumes when going out for many social occasions just so I don't contribute to occurrences such as that.