You might not have noticed it, but a key U.S. government protection that has been serving as a backstop for the nation's money-market mutual funds has just expired.

The temporary protection had been in place since last September. That s when one of the largest money-market funds, the Reserve Primary Fund, suffered a run on assets due to losses tied to an investment in Lehman Brothers. To keep that from happening again, the U.S. Treasury said it would guarantee deposits in money funds if they "broke the buck," or dropped below $1 a share in net asset value. A year ago, you could have the cleanest fund, the best-managed fund, but investors were taking their money out, and asking questions later, says Peter Rizzo, senior director of Standard & Poor's Fund Ratings and Evaluations Group. The federal guarantee calmed everyone down.

Now the program is over, as of Sept. 18. What will it mean for the nation's 38 million shareholders of money-market mutual funds? Here s a look at some key questions.

Are money-market mutual funds safe?

Despite the end of the blanket federal guarantee, much of the underlying assets held by money-market mutual funds continue to be covered by other government protections, says Peter Crane, president of Crane Data LLC, which tracks money-market mutual funds. Issuers of commercial paper, for example, are protected by the Commercial Paper Funding Facility and the Asset Backed Commercial Paper Money Market Mutual Fund Liquidity Facility, two other government programs implemented in October 2008 and in effect through February 2010. That s some assurance for investors with money-market funds holding commercial paper. Likewise, bank certificates of deposits, which are popular with money funds, are typically insured by the FDIC.

Should I worry that money is moving out of money-market mutual funds?

Assets in money-market mutual funds peaked in January 2009 at roughly $3.9 trillion, says Crane, and investors have been steadily pulling money out ever since. The amount in money funds stood at $3.45 trillion earlier this week, according to iMoneyNet s Money Fund Report. While some outflows may be tied to the end of federal guarantees, most redemptions are being seen as a sign of a greater appetite for risk among investors, rather than jitters around the safety of money funds, Crane adds. "A much larger risk is moving into bonds just ahead of when interest rates may rise," he says. "A lot of money has been moving out of low yields, and that kind of following the crowd usually gets you in trouble."

Should I go after higher yields?

It's true, the majority of money-market mutual funds are yielding almost nothing these days. But before jumping ship for a different money fund with a slightly higher rate, investors might consider whether slight variations are worth the risk, say some market watchers. Remember, money-market funds aren t where you go for yield, says Rizzo. If you see a fund paying slightly more than another fund, there s added risk built in somewhere. There is no free lunch.

How will the market react to the end of the Treasury guarantees?

Even though some money-market funds have already opted out of the program, its expiration will be an important test to see if the market has improved as much as people think it has, says Crane. Fund managers downplay the significance. At Federated Investors, the third-largest money fund manager by assets, executive vice president Debbie Cunningham says little reaction is expected. "It's not something that's sneaking up on people, she says. "Every indication is that it's going to be a ho-hummer."

Are there other changes ahead for money-market funds?

In June, the Securities & Exchange Commission proposed changes to the rules that govern money-market mutual funds. On the table are rules requiring funds to hold shorter-term securities of higher quality and new liquidity requirements. The president's Working Group on Financial Markets is slated to deliver a report about potential reforms this December.