I wrote about a study last year that suggested corporate earnings in the US could not grow by more than the growth of GDP.
"Our median estimate of the growth rate of operating performance corresponds closely to the growth rate of gross domestic product over the sample period ....the growth in real income before extraordinary items is roughly 3.5% per year" (after inflation and dividends. Before them it is about 10%.) "This is consistent with the historical growth rate in real gross domestic product, which has averaged about 3.4 percent per year over 1950-98. It is difficult to see how over the long term profitability of the business sector can grow much faster than overall gross domestic product. " (From a National Bureau of Economic Research Report by three economics professors: Chan, Karceski and Lakonishok).