Many of London's currency dealers have retooled themselves to trade more sophisticated products, such as interest-rate swaps and forward rate agreements.

ECONOMIST: Derivatives and foreign exchange

The Fed also extended its forward guidance for ultra-low rates, or outlook for interest rate levels, until mid-2015.

FORBES: METALS OUTLOOK: Impact Of Fed Action To Reverberate Into Next Week

That is, the interest rate on Argentinean short-term paper, or the price of the peso on the forward market, reflects the risk of a surprise devaluation that will cost you a chunk of your capital.

FORBES: Russian Roulette Investing

But pent-up loan demand in an economy that is seeing lower inflation and interest rates may imply a higher growth rate going forward.

FORBES