Since wind farms are cost competitive sources of energy, they appear to be an excellent alternative energy source for many areas. One issue critics point to is the obstruction large turbines have on people's views. I am skeptical that this type of externality has an impact anywhere near the impact from the byproducts of other energy sources such as burning coal, but that is a discussion for another day. In addition to costs associated with the obstruction of views, in many areas, land is scarce, so there may not be sufficient space for large wind farms. Additionally there are issues associated with the intermittent nature of wind sources and transmission. Conceptually, this makes offshore wind farms a good alternative for many coastal areas. Many offshore areas have considerable sources of wind and lots of space. At this point however, it appears that costs may be too high (hat tip Environmental Capital). Costs are being driven up by high demand for turbines and high material costs. That being said, wind, waves, and tides should provide a plentiful source of energy for many coastal regions, so once these technical and scale issues are accounted for, I wouldn't be surprised to see offshore wind farms become a part of the US energy portfolio.
On a side note, ecogeek has a post on floating turbines here.