Even though the US has never formally adopted a full-fledged new-Keynesian inflation targeting regime, its monetary policy was based on a closet version of IT that used the federal funds rate as instrument. There's little left from the preexisting Fed monetary policy framework, as explained in this The Economist article. Another The Economist article talks about how the new-Keynesian inflation targeting regime has become irrelevant in Switzerland too, where the Swiss National Bank has been forced to artificially depreciate its currency.
The reason why most of these countries have abandoned their different implementations of inflation targeting is simple: inflationary or deflationary expectations have become irrelevant as monetary anchors and stopped responding to the new-Keynesian monetary instrument of choice, the nominal interest rate. Inflation targeting was not only unable to avoid financial instability in all these economies, but, more importantly, revealed itself to be impotent exactly when effective monetary policy became essential (I'll return to this point in a future post).