John Hussman is one of the better market macro guys around and a favorite read. His latest is worth your attention.

“A practical note – as of Friday, our estimate of prospective 10-year S&P 500 total returns (nominal) has dropped to just 3.3%. With the exception of 1929, this level of estimated returns was never observed in historical data prior to the late-1990’s market bubble. Rich valuation is not a rally-stopper in itself, and we’ve certainly narrowed our defensive criteria enough to entertain a more constructive stance under some conditions without a steep market decline first. But the end-game here is still most likely a 30-50% market decline over the next 2-3 years, which would be far more than enough to wipe out any interim market gains. To dismiss that likelihood is to ignore predictable experience since 2000, as the bubble-bust cycle of easy money has repeatedly interacted with rich valuations to produce gleeful roller-coaster rides with very bad endings."