One of the features I love about my X5 is the ability to be able to lay out flat in the back and take a nap. If you've ever flown a red eye and found a row of unused seats in the back of the plane you know the sheer joy I'm talking about.
I often take the X5 on long motor trips and always throw a comforter and pillow in the back. I don't travel with the package shade, so if I need a rest, I just pull over, drop the rear seats and lay down in the back while she drives. I'm 5'11", and I easily fit diagonally. If I'm tired, there's nothing better than waking up rested and a 100 miles further down the road.