Worldwide Debt

This article from Robert Kiyosaki on Yahoo Finance is interesting and made me think of of how much debt many countries have. I can't imagine what would happen if China and all of the other countries we owe debt to came knocking asking for repayment. Of course this probably wouldn't happen, and taking our currency off the gold standard tried to prevent this, but it's still something to think about.

Should we be worrying about the size of our national debt? Is there something we should be doing personally to avoid these problems? Doing anything might be a bit alarmist, although I have heard of people buying gold bullion and such to make sure they keep something tangible.