As the once-mighty dollar continues to wane, it's proving a source of both risk and opportunity for investors.

The dollar's long slide has become a fixture of financial markets in recent years. Against the currencies of a broad group of trading partners, the dollar now stands at its weakest point in more than a decade.

The situation is even more dramatic with certain individual currencies. Earlier this month, the dollar hit a modern-day nadir versus the Canadian dollar and a 26-year low against the British pound. This past week, it touched a fresh record low against the euro. One euro now buys roughly $1.48 compared with just $1 five years ago.

Meanwhile, last week a new factor emerged to weigh on the dollar: talk that oil-rich nations in the Persian Gulf, which have pegged their currencies to the dollar for years, are reconsidering those arrangements.

Another Down Week

The dollar's recent slide is part of a broader worrisome mix that includes slowing economic growth and soaring oil prices and mortgage-related turmoil at financial institutions. These factors helped send both the Dow Jones Industrials Average and the Nasdaq Composite Index down 1.5% last week. For the year to date, the Dow industrials are up 4.2% and the Nasdaq, up 7.5%.