I play inverted (at least for Y) because I feel more comfortable "piloting" the camera rather than "controlling" it. You tilt your head back to look up. You pull the joystick back to look up. Which equates to down I guess. And speaking of which, I think I made that switch when game controllers started putting in analogue sticks. And I have my 360 set up to automatically make all controls inverted for the Y-axis. Everyone who plays on my console hates it though :} but screw 'em