Correction to this article

“I CAN'T decide what I like poking more: you, or these bubbles,” says bubble-blowing Kim Kardashian, a reality-TV star, in a new application for Facebook (see right). Cameo Stars, the company responsible for this innovation, lets Facebookers send to their online friends clips of minor celebrities mouthing generic greetings. Besides enriching the world's culture, the firm may also make a fortune. But gloomy types wonder if the profusion of highly valued internet start-ups with lighter-than-air business plans is evidence of a different kind of bubble.

For the first time since 2000, internet and technology entrepreneurs can raise seed capital with little more than a half-formed idea and a dozen PowerPoint slides. “There is probably a bubble in the number of start-ups,” says Alan Patricof, a venture capitalist, though he is not yet convinced that there is irrational exuberance in later-stage valuations.

Yet valuations have certainly risen, especially for the leading firms in this latest, “social” phase of the digital revolution. Groupon, a two-year-old firm that offers group discounts to online consumers, reportedly turned down an offer potentially worth $6 billion from Google, prompting analysts to ask if Groupon's founders had lost their coupons. A secondary-market auction of shares in Facebook in December had a minimum offer-price 77% higher than the price reportedly paid in a similar transaction three months earlier. Twitter is valued at $3.7 billion, up nearly fourfold in a year. The number of deals with (pre-investment) valuations of at least $100m is also increasing, according to Cooley, a law firm (see chart).

There are differences between today and the dotcom bubble of a decade ago. Then it was initial public offerings that were overpriced. Today, although the IPO market is reviving, it remains a shadow of its former self. Instead, the main way for the owners of a start-up to cash out is to sell their firm to a bigger one, such as Cisco, Google, Facebook or even Groupon. These tech-savvy firms ought to be less gullible than the stockmarket investors of 1999. But their owners may now be so wealthy that they care less about value for money than the coolness of owning the Next Big Thing.

The emergence of an active secondary market in shares of start-ups yet to go public has allowed founders and early investors in firms such as Facebook and Twitter to bank fortunes without waiting for a traditional exit by IPO or acquisition. These secondary-market prices feed hype about what these firms might be worth, were they to list on the stockmarket. Not many shares are available; many punters are chasing them. And those punters tend to be outsiders, such as fund managers and private-equity firms, who may not understand the tech business as well as insiders do.

Then there is the growth in “angel” investing, by rich individuals and small funds that provide seed capital to start-ups too small to interest a venture-capital firm. These angels make many small investments (say, $100,000 a time), in a strategy critics call “spray and pray”. That could certainly account for a bubble in start-ups. One prominent angel, Chris Sacca, has reportedly paused his investing on the ground that valuations have become overblown.

Other investors say this is alarmist nonsense. “For every firm that gets funded at a higher-than-normal valuation, a hundred are getting financed at a normal one,” says Ron Conway, a well-known “super angel” who has invested in many high-profile start-ups. Moreover, many young firms can tap into a thriving online-advertising market that was but a dream when the dotcom boom turned to bust.

Today's entrepreneurs also have a deeper understanding of the industries they are trying to transform, says Nick Beim of Matrix Partners, a venture-capital firm. Fewer of them are engineers. More are “ambitious non-technologists with a business idea” to change industries such as media, advertising, financial services or fashion. These industries are concentrated in New York, which is why the new boom is as much in Manhattan's Silicon Alley as in California's Silicon Valley.

Mr Beim reckons this industry expertise will mean that start-ups in “social commerce”, where there is a clear revenue model from the start, are more likely to succeed than those in social media, where no one knows where the profits will come from even when millions use the service (eg, Twitter). Three of the leading social-commerce firms, Groupon, Gilt Groupe (a luxury-goods seller in which Matrix has invested) and Zynga (a social-gaming firm), are increasing their revenues faster than any start-ups in history, says Mr Beim. That is why this time may be different. Of course they say that during every bubble.