here's Krugman's pronouncement from a persuasive piece called "the Keynesian moment:"
To be sure, Keynes failed to foresee the postwar rise of the “marginal efficiency of capital” — the way that economic growth combined with inflation would create an environment in which interest rates were high enough in normal times that monetary policy was effective at fighting slumps. Hence the long era in which Keynes didn’t seem all that relevant. But his analysis remained as valid as ever, under the right conditions. Those conditions reappeared first in Japan during the 90s; now they’re everywhere... And in the long run, it turns out, Keynes is anything but dead.