Few investors seriously worry about an imminent default by the U.S. or the U.K. But with worries about Dubai's ability to pay its debts shaking markets across the globe in recent weeks, investors are on guard about which other countries might be in dire financial straights.

Ratings agency Moody's, for example, said Tuesday that the upcoming year could be a rough one for government debt, issuing a report depressingly titled "Fasten Your Seat Belts: Tumultuous Times Ahead."

Anyone with access to the business pages knows individuals, banks, companies and governments everywhere have a serious problem -- just how bad it is and how long it will last is still being sorted out. Unfortunately, we probably still have a way to go before brighter days return.

Chris Nichols contributed to this report.

A “default” refers to a nation’s inability (or refusal) to repay its debt. Whether a homeowner sends “jingle mail” (home keys via post) because a lost job makes mortgage payments impossible or because a drop in home values makes paying the mortgage uneconomical, the effect on the bank is the same: they lent money and now they’re not getting it back.

“Sovereign debt” refers to the debt of nations. Just as the U.S. issues Treasuries backed by the “full faith and credit” of the government, other nations sell bonds in order to raise money to pay for programs ranging from armies to public healthcare.

Before you go thinking that problems can only come out from closed regimes or places economists have stuck with the "developing" tag, think again. Earlier this month, Spain's outlook was dropped to negative from stable by S&P, owing to fears the nation "will experience a more pronounced and persistent deterioration in its public finances and a more extended period of economic weakness versus its peers."

This week, S&P cut some of its ratings on America’s southern neighbor, but said the position is stable. Because the agency believes Mexico's attempts to raise money through sources other than oil revenue and to make the economy more proficient "will likely be insufficient to compensate for the weakening of its fiscal profile." Put it on your watch list.

Argentina, Grenada, Lebanon, Pakistan and Bolivia are judged to be a little better off, but they're saddled with still dubious B- ratings. The single-B classification at S&P means these nations are "more weak to undesirable business, monetary and economic conditions but presently the capability to meet financial commitments." Translation: Not good, and needs some things to go right, if possible soon.

Fitch Ratings last week joined two other ratings agencies in expressing concern about the country’s health. “Greece faces the possibility of falling under its debt,” Prime Minister George Papandreou said Monday in a speech where he pledged to slice the nation’s budget deficit by overhauling the nation’s tax system and cutting government spending.