This article from Wired Magazine (somewhat similar to this article from the N.Y. Times a month ago) seems to me to confirm that the present financial meltdown was caused by a sort of modern tulip mania, this time for collateralized debt obligations. A taste:

What is the chance that any given home will decline in value? You can look at the past history of housing prices to give you an idea, but surely the nation’s macroeconomic situation also plays an important role. And what is the chance that if a home in one state falls in value, a similar home in another state will fall in value as well?

Enter [David X.] Li…. Using some relatively simple math—by Wall Street standards, anyway—Li came up with an ingenious way to model default correlation without even looking at historical default data. Instead, he used market data about the prices of instruments known as credit default swaps. . . . It was a brilliant simplification of an intractable problem. . . .