Determine what a wall switch does
A lot of ceiling fan boxes are wired with two switches so that one switch can control the lights and the other can control the fan motor.  Of course, when someone replaces a fan, or even when it's initially installed, it's not hooked up that way so one switch controls everything.

After you check all the other outlets in the room (both sides like Chris said), you can pull the canopy trim off the fan and look at the wires.  See if there is an extra wire capped off in the box.