Generally speaking, I think the window seat should have control of the window shade, just as the person with the aisle seat gets to extend his/her leg into the aisle. On the other hand, I am usually happy to comply with any requests from my neighbors. The only exceptions to who controls the shade are during takeoff/landing (up), movies (down), and when the pilot says "if you look over the left/right side, you'll see..." (up). At other times, as others have mentioned, I think it is unfair to the window-seat occupant to keep the shade up, especially if the sun is glaring.