The correction we're seeing has been due for a long time. I personally don't think it has another 50%-75% to drop beyond where it has already dropped down to. I think that value investors (including lots of big $$$ institutions) will come in and scoop up some value plays with the new lower P/E ratios, providing a zone of support. This could happen either now, or after another 15%-20% or so decline. If the markets drop another 50-75%, you're looking at profitable companies with some insanely low P/E ratios---->the value investors/funds get giddy and go on a feeding frenzy. Also, in times of global uncertainty, foreign money pours into the US markets. As volatile as things are, the US markets are still seen as stable compared to most of the world.
But, I could be wrong...