SDS is one of my primary vehicles for shorting the overall market, and I use it extensively.

A word of caution though, it does NOT accurately track the SP500 at 2x inverse over time, and will deviate substantially given high volatility (check out the Proshares prospectus for details). This makes it a poor choice for holding “long-term” (plus, all short positions, regardless of vehicle, should be viewed as short-term trades). If you looking to hold for longer periods, Proshares has the SH ETF, which tracks the SP (1/x) to a better degree. This ETF is not leveraged, and trades thinly.