The benefit of winglets on airliners is more than just looking cool.
  Blended winglets like the ones you see on 737's actually increase fuel efficiency somewhere on the order of 4%, which is why so many airlines are paying well into six figures per plane to install them.  The aerodynamic benefits are many:
   With winglets, you can takeoff at a greater weight in any given conditions due to the increased lift they create.
   The increased span adds wing area, giving greater lift, which benefits not only takeoff and climb performance, but enables higher altitude cruise for any given weight, which equates to lower fuel burn.  This also gives the planes greater range and endurance.
  The winglets reduce the drag created by wingtip vortices at lower speeds. As the flow from the bottom of the wing tries to curl up and over the wingtip, it hits the winglet, creating further lift and in turn, avoiding the drag caused if the flow curls all the way over to the top of the wing.
  And oh by the way, they look cool.

  Skip Slater
  N540ES