Cash flow is the most powerful single factor in explaining cross-sectional equity returns (see references here). Like mean reversion 10 years ago, the question is, has there been too much entry? Is it done? In an interview with some anonymous trader, there's the suggestion that cash flow has been a key to the underperformance of funds like Goldman and AQR. Think again. Some factors are getting stepped on, but thusfare, Cashflow is not one of them.