It's been nearly eight years since the financial crisis, yet interest rates remain at recession-like levels. That's good news for economic growth -- but it's a dismal situation for conservative investors relying on income, including millions of retirees who don't want to take big risks to achieve a decent yield.

The traditional safe havens -- savings accounts, money market funds, CDs -- offer yields that are laughably low. Money market mutual funds investing in government paper currently yield only around 0.33%. Your bank may offer 0.6% on a money market account, which invests in corporate debt but is FDIC-insured up to $250,000. Five-year CDs pay 1.2%, which is a paltry annual return for the privilege of locking up your money for half a decade. And recall that these rates were even lower before the Fed raised short-term rates by 25 basis points (0.25 percentage points) in December.

Now, it's true that part of the reason that yields are low is that inflation has been close to nonexistent for years; some important goods and services -- such as gasoline, natural gas and flat-screen TVs -- have declined in price. So low yields haven't been devastating in terms of purchasing power. But for folks living off their savings who want to preserve principal over the long term, the prospect of low yields over the long term is troubling.