The dotcom crash of 2001 is a spectre that haunts anyone who makes their living on the internet. Those who work around what’s often called Web 2.0 are particularly sensitive about it because if another online slump materializes, that’s where it will strike.

But what will be the harbinger of a Web 2.0 crash? According to Dave Winer, that grand oldish man of blogs, RSS and OPML outliners, it will be signalled by the busting of Google.

… today we got the first rumblings of the shock that will signal the end of the bubble. Google stock will crash. That’s how we’ll know.

When I realized this, I should have known, because I’ve been saying for almost a year that Web 2.0 is nothing more than an aftermarket for Google. Startups slicing little bits of Google’s P/E ratio, acting as sales reps for Google ads, and getting great multiples for the revenue they generate by fostering the creation of new UGC to place ads on. When Google crashes, that’s the end of that, no more wave to ride, no more aftermarket, Bubble Burst 2.0. And the flip of this is also true — as long as Google’s stock stays up, no bubble burst.

Currently Google stock is riding high around $500 and forecast to go to $600 within a year. But stranger things have happened.

Now we hear this : “Google shares, which topped a milestone price of $500 a share last week, are overvalued and poised to fall, says Barron’s financial newspaper.

New.com reports : “Barron’s said Google is overvalued because it trades at 37 times next year’s expected earnings and because its growth rate is slowing.”

Is the bell already tolling for Google and Web 2.0?

Google shares have topped the $500 mark despite analysts scepticism, reports The New York Times.

“I thought the stock was a little expensive,” said Mark Mahaney, an analyst for American Technology Research and now for Citigroup said. “It turns out that was a terrible call.”

With forecasts of a $600 share price within a year, the Google fairy tale continues.

So by the beginning of last year, Mr. Mahaney jumped on the Google bandwagon. And so have most of Wall Street’s analysts, along with the portfolio managers who look after big pension and mutual funds.

Today, Google’s shares gained $14.60, or 3 percent to close at $509.65, passing the $500 mark for the first time. (Mr. Mahaney, whose sell recommendation came at $137, is now among those predicting that it will rise to $600 within a year.)

It has also been reported that Google is now worth half of Microsoft’s share cap, an astonishing rate of growth for an eight-year-old company.

Jeffrey M. O’Brien of Fortune Magazine writes :”The Web, they say, is leaving the era of search and entering one of discovery. What’s the difference? Search is what you do when you’re looking for something. Discovery is when something wonderful that you didn’t know existed, or didn’t know how to ask for, finds you. When it comes to search, there’s a clear winner — a $145 billion company called Google.”

If the Semantic Web (Web 3.0) is about making better sense of data and content, so that real people can use it, it will be an improvement on the dreary Web 2.0 stuff. Google has been at work on this for a while now — person-centric IPTV advertising (pitching adverts to a single person’s interests) is one of its major goals.

The new search engines will seek out connections and intelligent comments that have real meaning and value to the reader. Google is beginning to do this with its sidebars of extra choices within a search topic.

O’Brien says : “But there is no go-to discovery engine — yet. Building a personalized discovery mechanism will mean tapping into all the manners of expression, categorization, and opinions that exist on the Web today. It’s no easy feat, but if a company can pull it off and make the formula portable so it works on your mobile phone — well, such a tool could change not just marketing, but all of commerce. ”