Felix Salmon has an excellent article; here is one excerpt:
"The corporate CDO world relied almost exclusively on this copula-based correlation model," says Darrell Duffie,
a Stanford University finance professor who served on Moody's Academic
Advisory Research Committee. The Gaussian copula soon became such a
universally accepted part of the world's financial vocabulary that
brokers started quoting prices for bond tranches based on their
correlations. "Correlation trading has spread through the psyche of the
financial markets like a highly infectious thought virus," wrote derivatives guru Janet Tavakoli in 2006.