BOSTON (TheStreet) -- Among the consequences of the recent Great Recession were the flaws exposed in many target date funds.

The mutual funds were billed as a "set it and leave it" approach for retirement savings, built around an end date with investments that would switch from stocks to bonds as the years passed. Ideally, the funds simplify asset allocation and rebalancing while being immune to the whims of individual investors who might make rash, damaging decisions based on short-term stock-market movements.

Many of those with 2010 funds learned the hard way that the basic premise wasn't always followed, finding themselves with a larger-than-expected allocation to stocks that proved disastrous as the

Dow

fell by more than half in the months following

Lehman's

bankruptcy in September 2008. According to the Securities and Exchange Commission, funds with a target date of 2010 averaged 24% in losses in 2008. Hardest hit was the

Oppenheimer Transition 2010

fund, which shed 41% of its value. In 2009, returns continued to vary for 2010 target date funds, ranging between gains of 7% and 31%.

Despite concerns, the popularity of target date funds continues to surge.

Assets of target date funds registered with the SEC total $270 billion, up from $256 billion at the end of 2009 and $160 billion in December 2008.

Hewitt Associates'

(HEW)

annual study of company benefits showed that premixed portfolios, including target date and target-risk funds, now make up the largest portion of employees' asset allocations.

The jump can be largely attributed to increases in the number of employers using the funds as the investment default under automatic enrollment. Hewitt's research shows that among the 58% of employers automatically enrolling workers in 401(k) plans, 69% assigned them a target date fund.

Nevertheless, there are drawbacks to the "set it and forget it" approach. Because the funds are actively managed, they have higher fees those of index funds. Risk tolerance isn't customized by the one-size-fits-all strategy. And for investors who pick their own funds, there are plenty of mistakes to be made. One financial adviser recently commiserated about a client whose portfolio consisted of multiple target date funds in a misguided attempt to be diversified. The point of target date funds is that just one can satisfy investors' needs.

Investors need to be able to accept that target date funds are "boring and static" and not designed to be fiddled with, says Tom Lydon, president of Global Trends Investments and editor of

ETFtrends.com

.

"Investors sometimes get emotional," he says. "If you've got a 2040 fund, you are heavily invested in equities. And if you've gone through a bear market in the past five or 10 years, your fund has been negatively affected. You just have to understand that is what is going to happen. But, as the market goes through pain, there are many investors who just cannot take it anymore and say, 'I need to do something else.' "

Increased competition has led to new products, including the launch of target date exchange traded funds by

TD Ameritrade

(AMTD) - Get Report

,

iShares

and others, Lydon says. The ETF approach gives investors more options to choose from, attractively low fees and, with daily reporting, greater transparency.

The SEC and the U.S. Department of Labor have been reviewing target date funds to eliminate their shortcomings.

Last month, the SEC proposed rules that would require marketing materials for target date funds to disclose asset allocations among types of investments over the entire life of the fund. Funds would also be required to disclose whether the intended percentage allocations can be modified without a shareholder vote.

-- Reported by Joe Mont in Boston.

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