I just heard on CNBC that margin debt is at a new high.  Margin debt is money borrowed by investors (read:  speculators) to buy/short stocks.  It also means that the market rally is being fueled by credit.  This is ok as long as the market goes up.  But if, or I should say "when", the market begins to fall (and it WILL fall), the fall could be precipitious as folks rush to the exits to cover their loans.