I find the mood effect can be quite strong. Some scents are, for me, "joy in a bottle." And the effects of different scents can be very different, at least on me.
I've never heard of any scientific research into the effects, though I imagine there must be some. There were several popular novels in the 1980s that dealt with arcane aspects of perfumery but I don't remember they discussed this earlier. Even the perfume company advertising seems to draw only and rather monotonously on the power of scents to attract the opposite sex.