A team of researchers recently worked out that our current idea of "city as super-organism" isn't a good model for its behavior. Bigger organisms tend to be slower, and run through vast resources to maintain themselves. They found however, that cities don't follow this biological model. As population density increases, resource use in fact decreases, and output (in terms of wealth and ideas) increases.
Many of us sort of knew this already, but they were able to put it into the terms that decision-makers need to see: "Resource use is sub-linear, while output is super-linear." Those of you in the power-down, back to the land movement go right ahead and move out to the boonies. But as for me, I'm sticking around and choosing action such as working with the Oakland Food Initiative.
I think the goal and opportunity before us is to use cities' unique properties to uncover how to solve the problems cities do create.