The dollar plays a special role in the global economy because many commodities, from oil to gold, are dollar denominated. Hence, any weakness in the dollar makes those commodities more expensive.
Since the last G-20 meeting in Toronto in late June, when leaders talked about "collective well-being" and "shared objectives," the dollar has dropped 11% against a basket of currencies, driving up currencies in Japan, Canada, Brazil, the eurozone and elsewhere. With China pegging its currency close to the dollar, the dollar dropped a modest 2% against the yuan.
The American response to G-20 criticism was that the world needs a healthy U.S. economy, which means more U.S. exports. Most agree that the massive German and Chinese trade surpluses need to be reduced and better balanced achieved, but that doesn't help emerging markets. And with Bloomberg reporting that Japan's vice finance minister said the Fed's move could contribute "tremendously" to global growth, the summit could see a bit more accord on the issue.