Back in the days when Art Cashinand I might have taken Economics 101, we didn't talk about dollar depreciation because we used doubloons at the time.
But there was a truism then that holds true today and that is: no country has ever devalued its way to prosperity. Secretary Geithner even mentioned it the other day. The temptations of more robust exports with a weaker currency are tantalizing, but momentary. Not every country can grow its way out of a slump via exports. Unless world growth were so strong the tide lifted all ships. But to hope for that is naive, and countries know that. So the rush is on to put the pedal to the floor in the export car and criticize everyone else for manipulating their currency.
Right now the US should export more and rely less on internal consumer spending. China should export less and encourage consumer spending. For those two things to happen, the dollar has to fall. No US official will say it, but it's true. David Wessel says in the Thursday edition of the Wall Street Journal that, "The logic, drawn from the textbooks, is that a decline in the dollar (or doubloon) will make US exports cheaper for foreign customers, so they will buy more, and make Asian exports more expensive, so the world will buy less."