Reply #5: I think long term the flicker effect is larger concern.

[Statistical]

Reducing sound simply requires better engineering.
Also the sound energy is reduced at the square of the distance so tripling distance from turbine reduces the perceived sound energy by a factor of 9x.
Increasing setbacks, requiring more sound insulation, and better blade designs may be all that is required to resolve noise issue.

However if you have large moving object that blocks light and sun you will have flicker.
The flicker effect won't be reduced by distance. It is 100% up to the point where the shadow no longer falls on someones property.

Here is a video (about halfway through) showing flicker effect inside a house (1100 ft from turbine).
http://www.youtube.com/watch?v=MbIe0iUtelQ&feature=related

Computer models to simulate flicker effect based on GPS data and sat maps need to be developed and then instead of a static setback one needs to be developed that take into account the height of wind mill, path of sun, properties in the area, etc. Essentially something that will model the effect in the above video BEFORE wind turbines are built.

This is one major advantage of offshore wind (20 miles offshore). The flicker & noise fall upon nothing but waves.