A bit off thread, but I was in Nairobi recently and saw some Kenya Airways 737's with winglets: they were -700's, but their registration letters were in the same sequence the other, un-wingletted KQ 737's, so presumably a retrofit.
The winglets seemed to be at least 2 metres long and seemed quite out of proportion to the size of the aircraft.
Would appreciate any replies as to the benefits of "outsize" winglets. Also, I understand that the benefit of winglets is mainly experienced in the cruise, so how cost-effective are they for short haul operations?