This "1900 to 2000" trend people are extrapolating from is a myth. Stocks, as a broad category, have historically not been a great investment. Almost all the gain in that period happened in the last 20 years. If you break equity returns down into all possible 40 year periods returns were lousy.

This is taking the index numbers at face value. Better assessments of returns using good inflation numbers and incorporating tax liabilities make the picture much worse. http://www.itulip.com/realdow.htm

Finally, the real sample size goes back much farther than 1900. We have good equity price data back into the 18th century. 80% market crashes were common. Overall returns were not good.

Stocks were cheap in 1980. Then they soared in price for 20 years. Now people are slow to realize that period was exceptional. Investing is about "buy low, sell high" not "stick your money in stocks." Stocks are high. The smart money bought commodities in the early 70s, changed to bonds in the early 80s, changed to stocks in the early 90s, and changed back to commodities in the early 2000s. That smart investor has absolutely crushed an equity fixated investor. This isn't rocket science, either. It's not that hard to review asset classes once a decade and figure out what's very cheap and what's expensive.