"There is no such thing as aboslute safety. Any investment is safe at the right price, but risky at too high a price. The more you pay, the less safe it becomes"

Jason Zweig, The little Book of Safe Money, p 32

Billions have poured into bond funds over the past year. Are investors actually putting principal at risk when bond yields are so low? Are U.S. Treasuries offer a "risk free return" at current prices or do they really offer "return free risk"?