For the individual self builder, wind energy will seldom be a viable choice especially in an urban area. This is because the payback time on a wind generator depends on there being an ample supply of wind and a situation for the generator in which it can receive an unobstructed flow of wind from any direction. 'Ample wind' means the sort of place where there are few lulls in the wind, ideally you have to lean into it 24/7 for most of the year. 'Unobstructed' ideally means no buildings, or woods nearby and situated on top of a hill. Probably one of the worst places for a wind generator is attached to your gable end or chimney in town. There is constant turbulence around the roof of a house, cities are usually more sheltered and the noise and vibration is likely to be substantial. See Building for a Future - page 48 and Renewable Energy World's report. Very often the money would be better invested in higher levels of insulation and air tightness
See also Small scale wind turbines 1 - 6kW on the Greenspec web site
An excellent report, the Encraft Warwick Wind Trials Project, has recently been published on trials of 26 small scale wind generation installations. It shows the huge discrepancy between predicted energy output and what was actually achieved. The difference was mainly due to inaccuracies in wind speed prediction but manufacturers claims for their generators' power curves was also to blame.
The Energy Savings Trust has an on line average wind speed calculator and a sumary of the above report
One of the exceptions to the above might be if you are off grid and have no other means of generating electricity. One of the companies specializing in design and supply of off grid systems is Energy Development Cooperative Limited. (and their shop)
There are also developments in the pipeline for a more integrated approach to domestic generation in the form of Power Collective's Ridgblade. This is a horizontal cylinder turbine mounted along the ridge of a building's roof. This should be worth keeping an eye on. Vertical axis turbines are able to use wind from any direction without having to adjust and they tend to be quieter in operation. See the recent BSI award winning design by Ben Storan.
However, if you do live in a windy spot and you have space to erect a tower, it may be worth getting a survey done by a specialist company such as Sun and Wind. This may involve them setting up an anemometer to measure the wind speed for a year to make sure it is worth while. Neighbours can be hostile to proposed wind generators at the town planning stage.
Community wind power
This can indeed be a profitable option. An interesting example is the village of Fintry in Sterlingshire where they have invested in a large generator and are ploughing the income from it back into improving the insulation of the local housing. See the heraldscotland article
The Findhorn Foundation at Fores has 4 large wind generators which supply all of the community's needs with surplus electricity exported into the grid
Another interesting community based wind project is at the Hockerton Housing earth sheltered housing development. They actually have a link to a 'duel of the generators' where you can see the output of two of their generators compared.
Having been so negative about small scale generation it is best to say that there are some excellent small scale generators around. See, for instance, Wind and Sun's examples. Also, there is the added factor of the feedin tariff which has recently become available.
The Energy Saving Trust has a wind speed calculator based on postcode. It might be useful as an initial guide to viability of generating your own electricity from wind.