Remember when investors liked nothing better than dumping on the dollar? It seemed that quantitative easing by the Fed, at a time of higher interest rates in Europe and a surging China, would somehow lead to a permanently weakened greenback.
Currency investors are so over that.
(Read more: CNBC Explains: Quantitative Easing)
The prospect of aggressive easing and other stimulus measures in Japan is sending major investors out of the yen and into the buck, and "US dollar buying by Euro-based investors has also picked up significantly in recent months," says Samarjit Shankar, a currency strategist at Bank of New York Mellon.
One result is that the dollar index is currently trading at levels last seen "during the last major bout of risk aversion caused by the European sovereign debt crisis" last August, Shankar says.
A related result, according to the latest data on traders' commitments, is that in a rapid shift, investors now have net long positions in the dollar.