My parents were urban planners, and I had a pretty strong interest in urban history and planning issues for most of the first two decades of my life. I don't think about it much anymore I guess because it seems that most of what gets built has to conform to what people with money think should be built. And, at the very least, nowadays, people with money mostly seem to be wrong. Anyways.
The main things that the typical liberal planner would have complained about for the majority of the 20th century are been 1) the anti-social nastiness of most Modern architecture, and b) suburbanization. While, even during the current recession, trees continue to be cut down to build ever more ludicrous strip malls, even while old malls languish because it seems to be cheaper to build new than to renovate, the other trend of the last decade has been, of course, the re-urbanization of cities.
I am sure that I wasn't the first person to note all of the problems inherent in New Urbanism, and I did, many years ago (basically, it's cool that beautiful old buildings get renovated but it sucks because mostly wealthy people and corporations benefit. Also, culture is only approved of in the new city as a consumer pastime, not a protest). But I am not aware if anyone has discussed the ramifications for political organization. At least on the East Coast, no matter how bad suburbanization gets, there are still cities that act as the center around which the morass is "organized". Between the move of numerous mostly white and mostly rich people back into these centers and the housing crisis that seems to exist mostly outside of them, poor people are being banished physically to the margins. The obvious consequence of this has been the closing down of public space, both to protest, and even to certain types of people, but what warrants further discussion is the difficulty of organizing those that are now being moved outside of the denser areas, away from the best transportation, and out of the spotlight (even if that spotlight was only shined by the local media as a consequence of their work to make suburbanites feel justified in their exile). How will we reach these people? How will they reach each other?