NEW YORK (CNN/Money) - With the big-time rally stocks have seen this year pushing valuations back into the stratosphere, you have to wonder whether we learned anything at all from the busting of the late 90s bubble.

You would think that seeing such a massive amount of wealth wiped off their books would have made investors cautious about the market -- deeply mistrustful, even -- but that hardly seems to have been the case. Flows into the mutual funds are steady, online trading has picked up and casual conversation is turning back to what stock did what.

Even more distressingly, the stocks that have been doing the best are the sorts of highfliers that got investors into so much trouble last time around. Tech is leading the way, and for the tech stocks that are doing best, generating earnings is a future hope, not a present fact.

So naturally there are plenty of bears grousing on the sideline about how the bubble is reinflating.

Merrill Lynch chief U.S. strategist Rich Bernstein is one of them. In a recent note he pointed out that Vernon Smith, who won the 2002 Nobel Price for economics, has run trading experiments where participants consistently produced a bubble.

The funny thing is that after the first bubble, participants produce another bubble and crash. How come? Because they thought they would be able to cash out before the crash happened the second time around. In short, they end up playing the greater-fool game.

Which is what Bernstein reckons is going on right now.

Out of the laboratory, the evidence isn't quite so clean. Since the collapse of the Japanese stock market bubble, for instance, there have been many bear-market rallies -- some in excess of 50 percent -- but it is hard to say if those represented quite the sort of behavior Smith is talking about. Following the 1929 crash the Dow put on a huge rally and eventually gave back more than half of it. Was that the popping of a second bubble or was it Hitler?

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But regardless of whether these historical bubbles saw reinflationary episodes or not, they both saw a long time before they got worked out. It wasn't until 1954 that the Dow reached its 1929 peak again. The Nikkei is still trading near 20-year lows. In the meantime, both indexes saw periods where investors thought the coast was clear. It was not.