Robert Johnson has spent most of his career studying and teaching modern portfolio theory. So it may come as a surprise to some that Johnson, 57, has not a penny of his portfolio in bonds.

Johnson, president and CEO of the American College of Financial Services, said: "The absolute best-case scenario for bond investors is that rates remain low in the near future, which means your best hope is the status quo with no upside. If you lock in bonds at these levels, you're locking in a purchasing-power loss."