Robert Reich, writing for the New York Times:

Look back over the last hundred years and you’ll see the pattern. During periods when the very rich took home a much smaller proportion of total income — as in the Great Prosperity between 1947 and 1977 — the nation as a whole grew faster and median wages surged. We created a virtuous cycle in which an ever growing middle class had the ability to consume more goods and services, which created more and better jobs, thereby stoking demand. The rising tide did in fact lift all boats. As John Gruber points out, the accompanying infographic to this article is absolutely fantastic.