If you didn't know, there are ways to short the overall market without actually shorting the SPY, DIA, or QQQQ. All one has to do is buy the Proshares Ultra Short ETFs.
QID = Nasdaq
SDS = S&P 500
DXD = The Dow
The advantage (or risk) is that the ETFs will move twice as much and in the opposite direction of market it follows. The nasdaq goes down 1% and the QID goes up 2%. I bought some of QID shares on Friday.