Carmen came down this morning with a mouse in her hand, asking "Should this thing be hot?" She of course knew the answer, "No". I figured she needed a new mouse, but I got out a screwdriver and opened the thing up. It appears that a Zener diode on the backside of the board was overheating, which generated a rather sizeable black spot on the top of the board.
A trip to Target fetched us another six dollar mouse. If this one gets hot, I'll be suspecting the keyboard switch that she's plugging it into. If this wasn't boring enough for you, here are some more pictures of the board.