With short-term interest rates at historic lows, keeping large amounts of money in the bank doesn't seem the most attractive option for investors. Yet even as rates have fallen to 0.3% for six-month CDs this year from just under 5% at the end of 2007, insured bank deposits have risen steadily, says Todd DellaCamera, a managing director at Invictus Consulting Group, a firm that does stress-testing for banks.

This year, total insured deposits at U.S. banks totaled $6.5 trillion at the end of the second quarter, up more than $1 trillion from the same period in 2010, and up from $4.3 trillion in the fourth quarter of 2007, according to FDIC data. True, in 2010, a temporary law from 2008 that raised the insured deposit limit to $250,000 from $100,000 became permanent, but that change by itself doesn't explain the rise in insured deposits, DellaCamera says. Overall deposits - including uninsured - rose as well in the last several years, to $9.8 trillion at the end of the second quarter, from $8.4 trillion in the fourth quarter of 2007.

One explanation is investors aren't concerned about what kinds of returns they're getting - their top priority right now is safety, DellaCamera says. What's more, he says, with long-term rates compressing as well, investors aren't really getting paid to leave the safety of bank deposits.

"There's no premium to be gained by committing your money long term," he says. "A quarter of 1% may be an unattractive yield, but to commit your money for five years and not get a whole lot more than that" isn't appealing either, he adds.

There's an opportunity here for financial planners, DellaCamera believes. More than ever, investors need money management professionals to find investments that aren't too risky but will bring in more yield than low-interest bank accounts. As an investor, "you'd want a professional" to find, say, "the right corporate bond or mutual fund that doesn't pose a lot of credit risk."

One thing seems clear: When fear does leave capital markets and there's a hint of stability, all this cash sitting in banks "will be the first to be tapped for market reinvestment," DellaCamera says.