WSJ journalist Scott Patterson has jumped on the bandwagon suggesting that quants where a major cause of the GFC...
Conventional wisdom says that quants formulate models in conjunction with traders. Once developed they tell the traders how the model internals works, pointing out assumptions and limitations so that an informed opinion can be formed about when the model should be applied and when it's not going to work. Quants should be able to quantify the risk and expected loss under certain "bad" scenarios.
When the trading model is in operation, further up the chain back-office track exposures and risk, and at the very top bank executives have overall control of the allocation of capital to trading desks. Thus there are many levels of accountability: the quant, the traders, back-office, and executives. If people other than the quants don't understand the models and their application then they ought to be very caution about applying then.
I don't see that as a failure of quants. Sure, not all models are well thought out but in my mind it's a failure of risk management, or a strong preference by bank executives for profit over prudent risk management that is more to blame than the quants.