For buy and hold types, it is not a bad indicator along with looking at operating and reported P/E ratios, interest rates.
The fact that S&P 500 hasn't broken through 1530 is very scary. But the Dow Theory is still intact. The Transports and DOW still have not broken uptrend, although I think with GM, etc, the Transports may see decline. So, I stay put with stocks and money market for now.