"Nonetheless, if a bubble poses a sufficient danger to the economy as credit boom bubbles do, there might be a case for monetary policy to step in. However, there are also strong arguments against doing so, which is why there are active debates in academia and central banks about whether monetary policy should be used to restrain asset-price bubbles.
But if bubbles are a possibility now, does it look like they are of the dangerous, credit boom variety? At least in the US and Europe, the answer is clearly no. Our problem is not a credit boom, but that the deleveraging process has not fully ended. Credit markets are still tight and are presenting a serious drag on the economy..."