While looking at the CNU website I can across a fascinating artictle about slums, and that some possess inherent urban design strengths which planners can possibly learn from:
No one denies that slums – also known as shantytowns, squatter cities, and informal settlements – have serious problems. They are as a rule overcrowded, unhealthy, and emblems of profound inequality. But among architects, planners, and other thinkers, there is a growing realization that they also possess unique strengths, and may even hold lessons in successful urban development.
The article from the Boston Globe is here.
The article also references Prince Charles, who makes a similar point in a recent speech: Globalisation from the bottom up.
As an aside, I recall reading some time ago about reseach done in South Africa on how the layout of slums follow certian mathemetical patterns, even though there was intent on how they are laid out – an example of the phenomenon of emergence.