Shares of LinkedIn, the professional social networking site, more than doubled in their first hours of trading Thursday, giving the company a market valuation of nearly $10 billion. The "scorching hot" stock offering had been priced at $45 a share — already some 30 percent higher than initial estimates — and soared as high as $122 on Thursday. LinkedIn's stock market debut is the biggest internet IPO since Google went public in 2004, but "analysts are wondering if the valuations for stocks like LinkedIn are grounded in reality," says Evelyn M. Rusli in The New York Times. Is this a bubble?

Yes, this is a new tech bubble: The overinflated prices are "fueled by a desire to believe in Easy Street," and helped by the "PR hype machine" of private stock markets, says Erik Sherman at BNET. True, today's bubble companies have "significant revenue," unlike the startups a decade ago that just promised to "make money sometime in the future." But LinkedIn "has a major Achilles' heel: Most of its members don't actually spend much time on the site." So investors who are betting that the service will "grow like crazy" are likely to be disappointed.
"LinkedIn IPO inflates the tech bubble"

One stock does not make a bubble: "There's a big difference" between one risky stock and a full-fledged bubble, says Henry Blodget at Business Insider. LinkedIn has a real business with real revenue, and if it grows over the next few years, these prices could turn out to be well-deserved. Conservative investors may want to avoid the stock, but there's no reason to be screaming "bubble!" just yet. Save that for a time when "dozens of crappy companies with no businesses" are selling shares "at monstrous valuations."
"Sorry, LinkedIn's IPO is not proof of a new tech bubble"

Investors today are "a lot smarter," anyway: Investors learned from the '90s internet bubble, says Bob Pisani at CNBC. We no longer hear about silly metrics like "price-to-eyeballs." And while investors are focusing on growth and revenues, they will sooner or later demand that LinkedIn and Co. show a profit. That means that only "a small group" of stocks — like LinkedIn, Facebook, Twitter, and Groupon — will attract such frenzied demand for their IPOs.
"LinkedIn: A new era or a bubble?"