Fed Chairman Bernanke today said that the Fed's ability to provide monetary stimulus via lower interest rates was obviously limited (since the Fed funds rate today is trading at a mere 0.375%), but that doesn't leave the Fed powerless—they can simply buy bonds. That means the Fed will likely start buying bonds, and that news resulted in sharply falling yields. 10-year Treasury bonds now yield 2.7%, as they close in on their all-time low of 2.0% (1941), and 30-year bonds yield 3.2%, which marks a new all-time low (they weren't issued prior to 1977). Bond yields have fallen over 100 bps since mid-November.
And so we are witnessing what is probably the final chapter in the great bond market rally that began in late 1981. If you don't own any Treasury bonds, it's way too late to be a buyer now, since the upside is becoming extremely limited while the downside risk (e.g., what if the Fed overstimulates and pushes inflation up?) is becoming enormous.