Hurt most are the Swiss (who have been trying to intervene to depreciate the Swiss franc), and other peripheral European economies outside the EMS. Japan, with its own economic problems and a strengthening yen, took major unexpected unilateral action in mid-September: a massive (2 trillion yen) sell-off of the Japanese currency.
This has had some short-term effects on the value of the yen, but it angered other G-7 economies whose currencies are themselves at risk. In addition it has implications for other East Asian currency regimes, where countries under exchange rate pressure such as Thailand, Taiwan, South Korea and Philippines, could be encouraged to intervene.