I ran across this page on the Treasury’s website via Marc Cuban’s blog. It shows the yield on US government treasury bonds, adjusted for inflation. If the yield on a bond is 3% and inflation is 2.5%, the real yield is 0.5%.
So in inflation adjusted terms, anyone buying 5yr treasuries today is paying the US government 1.02% per year to store their money.
Curiously, after the downgrade, the world is paying the US government even more to store their money.