Ever wonder why we don't have more cute mixed-use cities like you see in Europe or Japan, with businesses on the street level and then some office space above, and people living up above, saving on commute and making for walkable cities?
Mostly it's due to extensive and complicated zoning rules that say what you can build where.
More evidence is coming out showing these zoning rules are hurting our economy, as well as potentially bad for the environment (because they lead to less dense living, and dense living is generally thought to be more environmentally efficient).
Last September, Obama called for cities to re-think zoning.
Here's a great starter article from Forbes on how America's zoning rules are stifling.
This blog has a lot of fun insights into zoning, with a great comparison to more efficient Japanese zoning.
(For a more hard-core look, see Fischel's book on Zoning Rules: The Economics of Land Use Regulation).