The dollar is king of the hill again -- at least for now.

Amid the cascading credit crisis, the U.S. currency has reclaimed its status as the world's haven in tumultuous times. With investors rushing to sell everything and shove the proceeds into dollars, the greenback has gained more than 11% against the euro in October alone. Since the spring, when the mortgage crisis picked up speed, the dollar has gained some 22% against the euro. It has also strengthened against the British pound, the Swiss franc, the Australian dollar and others, though it's weaker against the Japanese yen.

This reversal halts, at least temporarily, a longstanding bearish trend that had seen the greenback slide against major world currencies for much of this decade. Today's newfound strength has consequences for investors, consumers and travelers. A more robust dollar weakens the benefit of investing abroad, yet makes imports, commodities and even an overseas vacation more affordable.

"All those things that had been hurting the consumer have now reversed," because the stronger dollar is bringing down prices for oil and other commodities that had been pinching pocketbooks, says Liz Ann Sonders, chief investment strategist at Charles Schwab & Co. Still, she notes, the dollar's rise "isn't because we're in a fabulous economy. It's for mechanical reasons, as so much money around the globe is rushing to safety."

Indeed, the dollar could just as easily, and quickly, lose its current swagger. The greenback's underlying fundamentals were weak before the credit crisis began, what with elephantine budget and trade deficits and an inescapable date with looming Medicare and Social Security funding obligations. Today's crisis only amplifies the country's fiscal challenges.