Ok so I finally got around to looking at the wiring to try and figure out what's going on. In a nutshell: I have no idea what's going on.
I have a lightswitch that controls only one outlet, nothing else (as far as I can tell).
I pulled the switch out of the box, and found the following:
There are two Romex cables coming into the box. One has two wires (black and white) and one has three (black white and red). The two white wires are connected to each other, makes sense. The red wire is connected to the top screw on the switch. BOTH black wires are connected to the bottom screw of the switch. Huh?