Traditional Keynesian models, like the IS-LM one, were discarded as they lack micro-foundations. They were also subject to the Lucas critique (in the sense that one cannot properly estimate a macroeconomic model if the parameters respond to changes in monetary/fiscal policy).
While it appears that Quantitative Easing has reached its limits and the FED intends to implement a strategy of gradual exit, there is less clear what available options exist for stimulating the economy.
Some of the most prominent economists believe that inflation is a solution to the economic woes of US and Euro Area, and I particularly mean Krugman and DeLong. But is it so?