The S&P 500 closed below 850 on Wednesday, Jan 14, 2009. We have bounced off 817.04 on Thursday, Jan 15. We still stand a pretty good chance of testing the November 20, 2008 closing low of 752.44. All the major indices have broken down technically. They all could fall a further 5-10% from today's levels.
I would expect to see a 5-8% bounce off the lows before going lower.