As far as how bad is this downturn, to date it has been milder than I expected. But I personally don't think we have hit the bottom yet, especially in the stock market. Even with all the blood letting of the last 12-15 months, the price to earnings ratios of most stocks are still ridiculously high by historical standards.
I think US business productivity is going to take a major, major hit because of the new security concerns and expenses. For the same reason expect big rises in state and local taxes (the feds will bury their increase under deficit spending).
One major moderately influence in this downturn has been the fact that oil and gas prices have actually gone down significantly, primarily because the Russians were going contrary to OPEC. That changed in the last few days when the Russians agreed to sigificantly cut their exports. Expect prices at the pump to start rising in the very near future-and remember that retail gas/heating oil prices always seem to rise a whole lot faster than they fall.
My opinion, for what it is worth, is that we have not reached the bottom and there is a real potential for a major downturn ahead. More likely is more middling performance like the last few months, but least likely is the upturn predicted by the administration for this spring.