The Wall Street Journal and Dow Jones VentureSource count 65 venture capital-backed U.S. companies with a valuation of at least $1 billion, up more than 50 percent from a year ago.

That hefty number of "unicorns" may be a good thing for the companies' founders, but not necessarily for the rest of us, says Wall Street Journal columnist Justin Lahart.

"The private market is putting bubbly valuations on startups. What if the public market doesn't agree?" he asks.

"Pension funds, hedge funds and mutual-fund companies have been investing heavily in private companies, and any losses they bear could ripple outward. Given how much is now staked on private companies, the potential for losses is enormous."

One ominous finding comes from Sand Hill Econometrics research firm: overall private valuations now stand at about the same level as during the dot-com bubble of the late 1990s.

Valuations have been inflated by return-hungry investors who are eager to put money in while companies are still private, rather than waiting for initial public offerings.

"If fund managers who have been paying up for private companies start to think they have been playing the role of the proverbial greater fool, Silicon Valley's funding machine could freeze up. That could cast a pall on tech stocks and with them the wider stock market."

Meanwhile, Nobel laureate economist Paul Krugman recently offered strong criticisms of the technology industry in The New York Times, but he went too far, says software engineer David Auerbach.

"I am inclined to sympathize with Krugman when he bemoans the incessant empty hype around technology these days," he writes in an article for Slate.

"Disconnected venture capitalists, multi-billion-dollar valuations of content companies, millionaires telling us to check our privilege — it's all getting a bit surreal and a bit stupid."

But the problem is "complacent consumerism, not technology," Auerbach says. "If we hope to save ourselves from disaster, technology — real technology — remains our only hope. We shouldn't roll our eyes at it, as Krugman does. We should give it some credit."

Technology is vitally important for economic growth, Auerbach notes.

"In the next few decades, technology may play less of a role in fuelling major productivity gains, but it will play a far greater a one in preventing humungous productivity losses," he argues. "And by productivity losses, I mean ecological catastrophe, bio-destruction, infrastructure collapse and mass death."

That's why "Krugman's dismissal of technology's impact is shortsighted," Auerbach writes.

Related Stories:

• Bubble Watch: 'Biotech Valuations Are Always Too High,' Says Analyst Roy
• FT's Waters: This Time Might Be Different for Tech, But There Is 'Excess'