The document summarizes the remarkable and unprecedented expansion of the US economy over the past 9 years. It notes that the US economy has grown to be almost twice as large as at the start of the 1990s, while Canada only grew by a third over the same period. It attributes the US growth to restructuring in the 1980s-90s, flexible labor markets, record productivity, and huge investments in computers. However, it warns that the US private sector savings rate has fallen to unprecedented lows, leaving the economy vulnerable to a slowdown or recession if savings behavior changes. It draws parallels to downturns in Japan and other countries preceded by drops in private savings.