Center an object with inertia, regardless of it's registration point.

gistfile1.as

stage.addEventListener(Event.ENTER_FRAME, centerIt);

function centerIt(e:Event){

	var boundsRect:Rectangle = mc.getBounds( this );
	
	targetX = ( ( stage.stageWidth - mc.width ) / 2 ) - ( boundsRect.left - mc.x );
	targetY = ( ( stage.stageHeight - mc.height ) / 2 ) - ( boundsRect.top - mc.y );
	
	mc.x += ( targetX - mc.x  ) / 4;
	mc.y += ( targetY - mc.y  ) / 4;
}