There is only one reason the Great Depression became a decade of high unemployment and low output and that is because of government intervention into the economy. I have no doubt that the credit-filled boom will continue to morph into the credit-crunch bust, but there is no good reason as to why this has to turn into another Great Depression.
The ONLY thing that can make this current slowdown into a depression is government intervention and government spending. Paul Krugman continually calls for another "New Deal," which means he wants government to create cartels, limit output, and block the creation of wealth. If the government follows his advice, we WILL have another depression.
One wishes that the powers-that-be would listen to Ron Paul. However, a severe contraction also will mean that the politicians will have even more dictatorial powers, so it is in their best interest to make sure the economy tanks -- all the while blaming business for the whole thing.