It will be interesting to see where the coalition government goes on "mixed communities" which were such a strong, centrally imposed, feature of the planning regime under the previous administration.
Those of us who questioned the evidence base for this particular policy prescription suggest that there are obvious costs that may offset the (hard to detect) benefits. One of these is that specialised communities (e.g. just for the old or young) are better able to offer local services people want. If that sounds a little dry, Firhall, the "child-free" village in Scotland provides an interesting example.