This month, I've been doing a lot of thinking about the consequences of what some have termed the "hourglass" economy, in which there is growth at the low end of the income spectrum (a boon for dollar stores) and also at the high end (why else would anybody pay so much for a cup of coffee?). In a blog post over at the HBR site, I argue that one of the big problems facing Penney's, and many other organizations, is that the mass middle class is evaporating.