If US monetary policy settings remain too easy for too long, and if exchange  rates in China and the big surplus economies remain low even in the face of a dramatically improved economic outlook, we will risk facing conditions similar to those during the years leading up to the crisis: abundant global liquidity searching for returns in the wrong places, feeding unsustainable asset booms and growing economic imbalances.
Policymakers have become all too aware that government spending programs and tax preferences can be easy to initiate but extraordinarily difficult to shut down once constituencies develop that have a stake in maintaining the status quo.