The dollar and the US will not collapse in our lifetime.

The Euro.

Doesn't anybody remember that Iraq was going to switch from The Dollar to The Euro as it's currency to sell oil a few years ago? I don't remember the exact details but bad happen to them (Iraq). Something with booms.

Get rid of the IMF. That probably wouldn't be bad idea.  Get rid of the Federal Reserve and it's board of governors.  Definitely not a bad idea.  Let's do what we did prior to Nixon and back up our money with something that actually has value: gold, precious metals, etc.

A Federal Reserve note is just a piece of paper, guaranteed by our government.  The problem is, if the value of that note gets to a point where it doesn't buy anything, it becomes totally meaningless.  This is why I get frustrated with people when they complain that groceries are too expensive.  Hardly anyone realizes the dire consequences of what we're doing to our currency.  Printing money from a computer, adding additonal zeros to balance sheets to ease markets "quantitatively"... we're on a course for total ruin.  And people watch the news and think they have a choice in elections? lol.  Both parties support the total destruction of our currency.  Don't be fooled for a second.  You think you're being given a choice, but you aren't.  My only regret is not realizing it until I turned 24.

Military spending is not overly large as a proportion of GDP.  It is also miniscule when compared to health and entitlement programs, and will become smaller and smaller relative to those programs over time.

You may argue that that is as it should be, but lets not pretend that the military is in anyway the source of the USA's budgetary woes.

Hopefully soon.

^A lot of prognoses are made based on the assumption if there'll be a good substitution for dollar readily available. And what if not?

You would want to trade for a more stable currency.  The EU is the epitome of unstable at the moment.

Which is sort of the issue for the dollar.  No other currencies are remotely close to being adequete as a reserve currency.

If the US did get "replaced" very soon it would be, by no reserve currency at all.  (Or an internationally created one like the good ole bancor.)

to answer the op. The US Dollar will collapse as the world reserve currency when other currencies can buy petroleum.

I do think it's likely that the IMF could build a neutral currency, and horde a large fund of it as a middle-man for sovereign debt exchanges, or that some yet more complex multipolar order could emerge; such as a ¥€$ troika (an idea that was floated in Ghost In The Shell: Stand Alone Complex)

@ mai: a massive setback in the global financial markets, which will retard global growth for decades to come.

Part of the sability comes from everyone using it as a standard. 

If the USA goes into default then that would be bad - and we would see some major drama.  I would then if not the Euro it would be the Chinese Yaun for sheer volume.

I'm not refering to 'should' but 'more likely.'