Maybe I'm naive, but somehow I assumed that airlines replaced the pillow cases on those little white pillows after every flight. Not so much, it turns out. Airlines mostly use the time at the gate to re-fold the blankets and pick up trash. Ugh.
On another note, I recently bought one of those inflatable neck pillows, and it's really nice. Folds up to about the size of my wallet, and it's really comfortable if I only inflate it halfway.