We were in an aft cabin and it's not bumpy at all and it's wonderful. That was the best part about the room. As for people looking over, if they lean over their rail they can see you leaning on your rail. If you're reading a book in the chair, they can't see you. The advantages of the aft cabin are 1)you can see both sides in case of scenery just on one side, 2) extra large balconies, 3) the beautiful, peaceful view watching the wake of the ship.
We've got pictures showing the difference in the side vs the aft balconies. If you email us we can send you some.
Have a great time!