
Small eco-homes are not just a trend; they are the new era in real estate development. But they need to be built such that they can collectively share infrastructures the same way city residents do. The project I'm working on, applied to YC with (and was rejected from) last batch is built on this idea of more ecological homesteading in order to create better urban planning. Masdar City http://www.masdarcity.ae/en/ is an interesting prototype for the future of cities. We've schooled our youngins enough for them to know that ecological awareness needs to be a lifestyle. They're surprisingly aware that the world they are inheriting has exponential population growth, limited resources, and that the "industrial revolution" model of economic viability just isn't going to work forever they way it has been working.
Green Metropolis is an interesting read about big cities and sustainability: http://www.amazon.com/Green-Metropolis-Smaller-Driving-Susta...
Generally U.S. building codes include a maximum building height, and require minimum parking spaces. Many European cities have maximum parking spaces, and minimum building height. The latter produces higher population densities which make public transportation possible.
We need to push back against suburban sprawl and the car-first design. No required parking, no free curbside parking, and a carbon tax on gasoline. Once cities get a population density >7 people per acre, public transportation becomes viable. Population density follows a logarithmic curve with miles traveled per person, so you get as much of a reduction from moving from 2 to 20 people per square acre, as from 20 to 200.