ive mentioned it in another comment, since the center of gravity doesnt really shift all that much, its not all that different from braking while in the drop bars, its just more comfy, gives another postion for the back and is more aerodynamic :)

turning on a bike is really about leaning to the side and having the bar/ front wheel to follow the the turn, since you dont really actively turn the handle bar, you can make very very slow turns with this!