Winglets
For another authoritative explanation of modern wing design(with quite a bit on winglets) try:
Wing Aerodynamics and the Science of Compromise.
Jeff Jupp
RAeS Lanchester Lecture 10 May 2001.
I have heard Jeff described as the father of the A340 wing! His lecture explains clearly what factors are involved in modern wing design. He also makes it clear that although elliptical loading is the theoretical optimum for a wing of given span it is most emphatically not the optimum for a wing of given weight.