First thing I must state is that ANY currency system can come under financial attack, this is the nature of macroeconomics.
The biggest problem with currency, regardless of monetary system, is what *is* value. For an interesting read hit up the wikipedia article below.
The question is, WHY does our currency maintain value, despite printing craploads of dollars?
1. The dollar has a long and overall very stable history compared to other currencies. The brand US DOLLAR is right up their with Nike in *value*.
Just like how Nike prints a their logos on shirts made by slave labor for .50 cents a pop and sells them for $20.00 each, the US dollar does the same
2. Various international commodities are priced in dollars. Most countries selling oil take dollars, etc. To buy oil, you must convert your currency
to dollars, THEN buy the oil. This maintains demand for dollars.
3. Natural resources, running up a truckload of debt is no biggie if your debt is a fraction of the overall value of your iron, steel, trees, wheat,
oil etc. The sheer physical size of the US with its massive resources helps guarantee payment on any US monies. Even with collapse their is a LOT of
value in this country. Running up a million dollars in debt is no biggie for an individual with a 500 million dollar home. Our relative value gives us
a LONG line of credit, no country has as extensive of natural resources as us outside maybe Russia or China.
4. Attractive debt instruments. Stocks, treasury bonds and everything in between. The US uses interest rates balanced against unemployment to control
inflation. When unemployment gets to low you risk deflation, when too high you risk inflation. You can lower the number of transactions by increasing
unemployment by increasing interest rates which causes more defaults etc., thus indirectly controlling inflation/deflation through unemployment. By
controlling the lending rate the US has been able to offer attractive, stable returns over the long term. Additionally, foreign countries have bought
up large shares of US businesses since the late 70's/early 80's, this makes it in the interest of countries such as Japan and China to help maintain
stability in the US as our loss, would be their loss.
*note* Our system CAN NOT function with full employment, the unemployed also help drive up the value of your currency.
These are just a few general bits of information, I'm sure others will ad more.
*note* Like the directness of your answer Rockpuck better than mine!