A strong currency reflects booming commodity exports and sound public finances. But not everyone is cheering. IT HARDLY came as a surprise when, on September 21st, the Canadian dollar crossed a symbolic threshold and overtook its American counterpart in value for the first time since 1976. Since January 2002, when Canadians needed C$1.61 to buy a greenback, the loonie (so nicknamed after the aquatic bird depicted on the dollar coin) has been pushed up by world demand for Canada's commodities. Yet even hard-bitten currency traders cheered out loud as the loonie inched towards parity, and then beyond. David Watt, a...