Check out this Video from ted.com about sustainability in the United States and developing countries!
Alex is right that we do need to make changes to live more sustainably. The fact that the amount of energy we are using equals 4-5 planets is outrageous. City life does need to become more sustainable through transit systems and sustainable buildings, and the resources that the United States has is making it easier for companies and people to make sustainable choices.
However, I think that his opinions on focusing attention on developing countries to become more sustainable is unnecessary at this time. It is important that the world uses less energy and reduces their carbon footprint, but these countries should focus their attention on improving their political and economic situations. Yes these sustainable technologies are ideal for developing countries, but who's to say that they would accept and use the technologies Americans are forcing on them.
I feel that it is more important to focus our attention on our country. The United States is the country that is using the most energy consumption. And so, we should focus the attention back on ourselves to make the changes before pushing our ideals and values on other countries.
You can also check out Alex Steffen's website worldchanging