How much did low interest rates matter?

It is popular to attribute the credit boom (at least in part) to the Federal Reserve having kept the federal funds rate "too low for too long," but comparison of the path of the funds rate in Figure 5 with the measures of credit growth in Figure 1A shows that the increase in lending was greatest in 2006 and the first half of 2007, after the federal funds rate had already returned to a level consistent with normal benchmarks.

That is Michael Woodford from the Journal of Economic Perspectives.