This quote from the FT.com encapsulates the key reason why both Jack Weyland and Justin Uyehara have used TWM, a double inverse the Russell 2000 ETF to hedge their portfolios from time to time.

FORBES: Why TWM Makes A Good Hedge

The UltraShort Financials ProShares moves at a rate double the inverse of the Dow Jones U.S. Financials index.

FORBES: Magazine Article

They are designed to double or triple the performance (or the inverse of the performance) of the target index when held for a day.

FORBES: Confessions Of Leveraged ETF Lover