What's an education worth?

New York Times’ Economix:

…it’s harder to make it in today’s job market than it was a few decades ago if you don’t have at least a high school degree, since the expectations for what educational credentials workers should possess have risen. This is in part because the economy is less dependent on lower-skilled, manual-labor-intensive industries like manufacturing, and more reliant on industries that require formally credentialed education and training, like health care. Thus, in general, the earnings potential for the most educated has risen, and that for the least educated has fallen.