What role do the winglets on the next-generation 737 play? I've flown on a couple of 737's recently and noticed that the wings are quite beautiful and have a distinctive upward sweep at the wingtip, almost like a vertical stabilizer.

What advantages and what disadvantages (if any) does this type of wing provide?  I imagine there is some gain in overall stability.
The wing tips calling as "sharklet" at Airbus A/Cs and "winglet" at Boeing A/Cs. It reduces the tip vortex and helps to prevent from airflow seperation at wing tips. It have positive effects on both fuel consumption and turbulance making. Negative effect of the additional part is increase of the drag coefficent but you can keep it negligible againts the positive effects.