Depends on how the world responds to this move. It will make U.S. exports and services cheaper for the world to buy, but it will also make imports more expensive. I don’t think the amount of devaluation from they will achieve will be nearly sufficient to attract businesses/manufacturing back to the U.S.

Politically it is useful in that it forces foreign nations whose currency is fixed to the dollar to spend their foreign reserves in order to maintain their pegged exchange rate – basically it forces China, to spend their currency reserves to maintain their peg. This decreases the amount of conomic leverage China can have over the U.S. In the case of the U.S., it should cause the value of dollar-denominated assets to decrease and may cause capital flight from the U.S. All those investors that are dumping U.S. assets are going to invest their money in other countrys’ assets causing an increase in inflation in those countries which are destabilizing for their respective economies. This is happening now. If the world market interprets this move as a sign of U.S. weakness and Fed desperation then the dollar will continue to fall and will probably lead to U.S. economic collapse. If the market sees this QE as a Fed tactic to force other countries to revalue their currencies, then the markets may not react so sharply. Without knowing all the details, it’s hard to tell whether or not this will ultimately help or hurt the economy. It’s risky for sure, but it really depends on how much confidence investors around the world have in the U.S. to pull off this strategy.