Look what happened to investor margin debt (from the WSJ–link):

Hungry Investors Boost Margin Debt

By GASTON F. CERON

A rising stock market encouraged investors to go into
debt to trade stocks, leading to an increase in the level of so-called
margin debt in 2006.

Such debt is accumulated by investors who trade "on
margin" with funds borrowed from their brokers. As tracked by the New
York Stock Exchange, margin debt rose to $270.52 billion in November
from $221.66 billion at the end of 2005, the first time in more than
six years that margin debt has topped $270 billion. December numbers
will be available later this month.

That 22% increase left margin debt not far from the
record of $278.53 billion, reached in March 2000 as the Nasdaq
Composite Index was setting a record high. Last year’s rise in margin
debt occurred against a bullish backdrop for stocks, with widely
followed market indexes notching double-digit percentage gains.

Market analysts track margin-debt activity as an indication of investors’ appetite for speculative trading.

A potential pitfall for those trading on margin is a
sharp decline in stock prices, which can expose investors to margin
calls, requiring them to post additional collateral or see their
brokers sell their securities. Some market watchers consider high
levels of margin debt worrisome because a wave of margin calls
triggered by a sharp market decline could exacerbate the selling
pressure on stocks.

Hat tip: Daniel Gross.