Diane Coyle has a great post reviewing various books about the future of cities. This is the money quote for me:
Is this the dawn of an era of powerful cities and weak nations — much like the age of city states half a millennium ago? It seems highly likely. More than half the world’s people live in urban areas now. Most economic activity consists of trade in ideas and people and goods and services between cities. Mayors are important figures, who for the most part feel less bound by the constricting conventions of national party politics. As ever, though, political and social institutions lag behind technological and economic trends, and in centralised polities like the UK urban renaissance would involve some big changes.