A good strategic question raised by Tony Jackson in the Financial Times commenting on a Morgan Stanley forecast - "The present downturn is neither the Great Depression nor Japan because (in essence) all previous mistakes have been avoided this time." Tony is correct to observe that this assumes that all possible mistakes were contained in those two economic episodes and none of today's policy actions will later turn into new mistakes. (Japan once famous for poor quality imports, then highest quality DRAM memories, and ultimately all manner of cool consumer electronics is now famous for a never-really-ending deflationary stagnation).
As for the Great Depression, all we have are history lessons. No one alive today was old enough in 1929-1932 to understand what was happening. Paul Volker, Obama's new Recession advisor, was in diapers in 1929. Recently I tried reading the Financial Times to my 3 year-old granddaughter, but I don't think a single word sank in. A lot of help she'll be when the "Economic Disaster of 2090" occurs.
A world economy of $80T with 4B consumers, and 1B investors, all connected to online information and complex trading systems. But with different goals, strategies, political, emotional and cultural bias. In other words (to paraphrase Black Swan theory), knowledge of past events cannot perfectly prevent tomorrow's surprises. That's why they're called surprises. At least the smartest people are (gathering) in the room.