The five ceiling fans in my Southern California house are on virtually nonstop, night and day, from July through September. I haven't done analysis, but anecdotally they make rooms feel a lot cooler. If you get quality fans, they are inaudible (at low speed) and seem to be trouble-free (i.e., no problems after ~10 years of this level of activity).
Brushless AC motors (short circuit cage type) are extremely reliable, there are only two things that can happen: eventually the bearings will run out or the coils will short due to the mechanical friction resulting from the changing flux which tries to push the wire around. The stators are usually cast into a resin to counteract this as much as possible but in spite of that some freedom of movement usually remains.
