It's how big it is and what you do with it

"On Mar. 28, the state-run China Business News reported that the mainland's reserves hit $854 billion in February, outstripping Japan's reported stockpile of $850 billion."

So, combined, that means Japan and China own US$1.7 Trillion of US debt. Awesome, Dude.

China and Japan have propped up the value of the dollar and financed U.S. spending by continuing to absorb U.S. debt via the purchase of Treasury bills. Yet these purchases have sown unease, with some in Washington complaining that the United States has relinquished control of its destiny to foreigners.

"The U.S. could fear concerns that as China possesses U.S. debt, that could give China the ability to influence the U.S. financial situation," Shen said.

See also http://guambatstew.blogspot.com/2005/10/its-not-how-big-it-is.html