I would say almost all keep their reefs at 78-82. I used to keep mine 78-80 (but it would run up to 82 in the summer), I have been doing more reading on this subject and I may bump it up to 80-82. Has to do with coral growth, closer to actual reef ocean temps.
Like sparky said, I also keep mine at 78 (this time of year), but when lights go on and the ambient room temperature rises during the day it'll hit 79-80. In the dog days of summer it'll hit 82-83. If I see it hit 84 lights are off. My fan goes on as soon as the tank hits 80.