Erik Bryonjolfsson claims it's productivity:
[P]roductivity, output per unit input, is by far the most important determinant of our living standards. As Bob Solow showed in his Nobel Prize winning work, the main thing that makes an economy richer is not working harder or even using more capital or other resources. Instead, the main driver is innovations in products, services and business processes that let us create more value without using more inputs.
He admits that "not everyone is benefitting from strong productivity growth," a point he apparently addresses at length in a new ebook he co-authored.
The Dish 
