Aesthetic impacts -- Some people do not like the visual appearance, though some do appreciate the turbines.

Bird kills -- Sometimes birds are killed by flying into the rotors.  This can be a huge problem because it decreases the bird population and may cause wind farms to violate the Migratory Bird Treaty Act or the Endangered Species Act.  Scientists are working on ways to deter birds from the turbines. 

Intermittent nature -- Wind is not a constant resource and wind power cannot be stored without batteries.  Wind power is not always timed to meet electricity demands.  The continuing advancement of fuel cell technology should help the energy storage issue.

Transmission -- Wind farm sites are often located far away from the bulk of the electric power demand.

Competing land use -- Wind resources may compete for the land.  However, wind farm land can have a dual purpose:  electricity generation and grazing or farming.