What if the Internet sector has already started to go south again? What if the good times have already sailed past, well before we got a chance to figure out what exactly "Web 2.0" was supposed to mean?

These are not very welcome questions, not with profit and revenue growing at Internet stalwarts such as Yahoo! ( YHOO) and Google ( GOOG - Get Report).

But because Friday marks six years to the day of the end of the Internet's first big wave of growth, it's a timely question. Anyone who held on to stocks like Ariba , Infospace ( INSP) and VeriSign ( VRSN - Get Report) through 2000 and into 2001 -- hoping that they would bound back to new highs -- doesn't want to be in the same situation on that spooky anniversary.

(Even after rebounding some in the past few years, Ariba is still 99% down from its record high, while Infospace is down 98% and VeriSign has tumbled a slightly more moderate 91% -- each a smelly albatross hanging around the necks of those who pounded the table for these stocks in the weeks before dot-com stocks peaked.)

Now, in sober contrast to the sector's rally in the closing months of 2005, Internet stocks are uneasily down. As of Tuesday, Yahoo! had lost 28% in the last two months, Google was off 23%, eBay ( EBAY - Get Report) is down 17%, and Amazon.com ( AMZN - Get Report) lost 22%.

Even more recent upstarts that teased Wall Street with the promise of brave new industries were hammered for earnings that are growing, but just not growing fast enough for Wall Street's appetite. XM Satellite and iRobot ( IRBT - Get Report) dropped 17% and 29%, respectively, on their first-quarter earnings reports.

More disturbing still was the market's reaction when Google's CFO pointed out something mind-numbingly obvious: As the company gets bigger, its revenue growth rate will slow. That mild-mannered factoid cost Google $17 billion in market cap within 30 brief minutes -- and in the subsequent week the stock has recovered less than half that loss. (Although, who knows? Maybe investors were simply stunned to learn that Google had a CFO who could talk.)

Another bit of sobering news was that the Internet's reach just can't keep growing like it used to.

Last month, research firm Parks Associates said the percentage of American homes with Internet connections would grow this year from 63% to 64% -- one whole percentage point. That's not exactly what one would call penetration -- it's more like a gentle poke.

There are only 39 million U.S. households without Net access, the research firm notes, and it seems that only 8 million of them have a computer. Parks Associates director John Barrett points out that this is a problem of demand, not supply: You can throw in all the cheap PCs you want; they just don't care. One-fifth of the unwired masses claimed they simply are "not interested in anything on the Internet." No, not even World of Warcraft.

It can't be happening already, can it? Can the Internet's second wind be gone so fast? The first wave of the Internet's growth, lasting from Netscape's IPO in August 1995 to the Nasdaq's topping out at a still giddy-looking 5132.52, took nearly five years. It's only been three-and-a-half years since the Nasdaq bottomed out at 1108.49 in October 2002.

One of the tenets of what used to be called the "New Economy" is that, thanks to just-in-time inventories and more sophisticated scrutiny of economic data, boom and bust cycles are growing less volatile, and shorter. If that's the case with the economy at large, why can't it be true for Internet investors as well?

So maybe this spirit of moderation isn't such a bad thing. Rather than prolonging the Internet rally with hypnotic chants of "The rules have changed," investors have remained a little gun-shy about less-than-stellar earnings numbers -- which may just be, in the long run, a healthy thing. Sure, markets are down this month, but if that means staving off another mania, what's wrong with that?

Not only is demand more in check, supply is also greater than it was five years ago. Stocks of pure-play Internet companies are also more plentiful this time. About 62% of Google's 296 million outstanding shares are available for trade, as are 86% of Yahoo's 1.46 billion shares and 74% of eBay's 1.41 billion shares.

When the last Internet bubble burst, a few cool heads predicted that it was merely the market's blind enthusiasm that would be swept away --the Internet technology itself would continue to improve. They were right. Enthusiasm for Internet stocks came back last year, but it looks like it's not blind this time. Shortsighted at moments, maybe, but not blind.

If tempered enthusiasm means less volatility, that may be the best news investors in Internet companies are going to get this month.