Rob Walton (Walton Family Foundation/Wal-Mart) and Peter Seligman (Conservation International) are at the Aspen Ideas Festival offering insights on scaling sustainability.  These lessons (some stated, some embellished from their remarks) seem to apply to urban leaders working to get smart ideas for next generation cities to a tipping point:

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At his always interesting blog, The Bellows, Ryan Avent poses the fascinating question, How many talented people would have to move to Detroit to create a tipping point that becomes a self-sustaining movement?  What started as a Twitter joke ("Let's all go buy a mansion for a $1.") turned…