Alert! Stock funds gained assets four weeks in a row, picking up $20.7 billion through January 30.

That has not happened since April 12, 2000, according to Lipper head of research services Tom Roseen.

Investors, he said, are pulling out of money market funds, for instance, and putting savings back to work in both equity and fixed-income funds.

They're even getting on the "risk train,'' he said. Roughly $1.2 billion got put into emerging market funds.

All told, the return for the average stock fund hit 4.82% ... for the month. Heady stuff.

But let's not get carried away here.

In this century, when stocks start to rock, it's time to start worrying.

Let's look at the "magic" number that popped up at the end of January.

The number was 1,500 and the index was the Standard & Poor's 500. That is almost exactly double its value of 735.09 at the end of February 2009.

But that 1,500 milestone bears caution. The first time it was reached was in August 2000, finishing that month at 1,517.68. The dotcom bubble was already in the midst of bursting.

By the end of February of 2003, the index was sitting at 841.15, a 44.6% drop.

The next time the index hit 1,500 was in May 2007 and by the end of October the index was sitting at 1,549.38. Then came the plunge still fresh in memory. We all remember the credit crisis, right?

By the end of February 2009, the index was down to 735.09. And mainstream investors wouldn't touch stocks again.

Until last month.

Sure, the Purchasing Managers Index looked good in Asia, Europe and America. Sure, 68% of S&P 500 companies are beating expectations on the bottom line, as Roseen notes.

But something's missing. The boosts to the bottom lines are not creating corresponding boosts in employment. The Fed is still committed to its nearly-no-interest-rates stimulus through 2014. And baby boomers-now retiring-must keep working, long past the norm, to survive.

Most critically, somewhere not very far down the road, the U.S. will have to stay paying down its bills.

Maybe we've just seen the first sign that the next debt crisis really is upon us.

Subscribe Now

Access to premium content including in-depth coverage of mutual funds, hedge funds, 401(K)s, 529 plans, and more.

3-Week Free Trial

Insight and analysis into the management, marketing, operations and technology of the asset management industry.