My gardenias came into bloom last week. I have a love-hate relationship with them. I love them because they're low-maintanence, elegant plants with beautiful, pinwheel-like flowers and an exotic, tropical, seductive smell. I hate them because more than a few moments in the same room with them can be too much. (I have a bunch sitting less than a foot from me as I type, and I have breathe through my mouth.) As they bloom then decline, their scent goes from exotic to just plain slatternly and strident. What's more, they don't drop, and I have to deadhead them daily or my bushes are covered in brown, gnarly-smelling blossoms.
As white flowers that bloom during the dry period, they're also constantly under attack by scale and the subsequent black soot. (Scales, tiny insects whose excretions create the ideal medium for black, sooty mold, are attracted to white flowers, particularly magnolias and gardenias.) It's fairly easy to deal with the disease, though: Soap spray and a blast from my watering gun.
Interestingly, I bought two (genetically) identical bushes (grafted Miami Supreme) two years ago. One gets a lot more sun, and seems to suffer more from the scale and mold than the other, which is in partial shade. What's more, the one in more shade is generally healthier (thicker trunk, fuller shape), with deep green leaves and abundant blooms. Supposedly gardenias should be planted in full sun, but my experience indicates otherwise.