This article by Kou Xin et al. (link) studies a “Compliant Adaptive Leading Edge” for UAV wings. It is indicated that compliant trailing edges can enhance the lift-drag ratio by 5∼15%. A rather interesting aspect of the article is that the resulting structure is actually built out of aluminum and tested. I cannot recall seeing another example where a compliant structure was built out of metal. The results seem to be satisfactory, the deflected shape conforms to the aerodynamic goal set before. 
However the fatigue life of the structure is not tested, which is crucial for such applications.