This is what the JPMorgan Chase investor newsletter, Eyes on the Market, of July 11, 2011, had to say on this question:

[P]rofit margins have reached levels not seen in decades. The challenge, which we have discussed many times before: what is driving these margins? One useful way to deconstruct profits is to measure them from peak to peak, and analyze what changed. As shown in the first chart, S&P 500 profit margins increased by 1.3% from 2000 to 2007. There are a lot of moving parts in the margin equation, but as shown in the second chart, REDUCTIONS IN WAGES AND BENEFITS EXPLAIN THE MAJORITY OF THE NET IMPROVEMENT IN [PROFIT] MARGINS. This trend has continued; as we have shown several times over the last two years, US labor compensation is now at a 50-year low relative to both company sales and US GDP (see EoTM April 26, 2011).

Note that this analysis only goes through 2007; it's far worse now. U.S. corporate profits are at record highs, despite the depression economy.