The problem with wind turbines so far.
As I understand it, the issue is blade maintenance. The things get hit, nicked, bent, or otherwise abused and don't last as long as one would like.
Now I don't for the life of me understand why turbine blades in hydroelectric dams last as long as they do. Those suckers are spinning, fast movers, and I would think they'd be vulnerable. I don't thing the water is filtered all that well.
Arf