Henry Blodget, the ex-analyst who now presides over Business Insider, wrote in a blog post today that Facebook shares are probably worth $16-24 a share; use the midpoint at $20, and you’ve still got a potentially massive slide from today’s close at $34.03. (Which of course is down from the $38 IPO price.)

Blodget reached that conclusion largely by applying a valuation of 20-30x estimated 2013 earnings of 80 cents a share – a level that is actually above the Street consensus view at 60 cents.

The basic point is that at $34, the stock is trading at 57x the current 2013 consensus, or 43x the more aggressive forecast Blodget is using in his calculations. That level, Blodget argues, seems unsustainably high. And I find it hard to argue with him.

Let’s compare Facebook’s valuation to those for other high-market-cap tech companies:

• Apple: 10.4x September 2013 fiscal year earnings estimates.
• Microsoft: 9.8x June 2013 fiscal year estimates.
• IBM: 11.9x 2013 estimates.
• Google: 12.1X  2013 estimates
• Oracle: 10x May 2013 fiscal year estimates
• Cisco: 8.6x July 2013 fiscal year estimates.
• Intel: 9.7x 2013 estimates
• Amazon.com: 86.2x 2013 estimates.

To buy Facebook at the current valuation is to think that the company can sustain the kind of dramatic high valuation sported by Amazon or by the smaller-sized ($21 billion market cap) Salesforce.com. But that seems like a highly risky bet.

Facebook is growing faster than most of the companies on the list (although slower than Apple) but it also has a lot shorter track record and a lot more uncertain growth path ahead. IBM isn’t growing the top line, but we also know that their business isn’t going to disappear for a long time to come. Microsoft is
In short, there are many very reasonably priced plays on the future of the digital economy. You don’t need to own Facebook, which trades at a massive premium to almost every tech company of comparable market cap. There very well may be a time to jump in to the stock, given the company’s vast user base and remarkable role in the social interactions of hundreds of millions of people. But current valuation suggests this is not the time.n’t the fast growth company it once was, but it also has promising new products, a mammoth cash pile and a cash generation machine in Windows and Office. Apple may already be the largest U.S.-listed company by market cap, but it is continues to produce astonishing growth, particularly in China, where the opportunities for the company remain vast. And so on.

Update: The venture investor Roger Ehrenberg wrote in a blog post last week that the Facebook IPO reminds him of the initial offering a few years ago for Blackstone Group – which came public in 2007 at $31, jumped to $35 on offering day and “has been worse than dead money every since,” now trading at about $12.

“Like Blackstone, [Facebook is] a great company and a leader in its field,” he wrote. “Also a beneficiary of scarcity value given that there isn’t a public company quite like it that represents an opportunity for institutional or retail investors. And while its principals might not be the market-driven sharks like those running Blackstone, their investors firmly fall into this category. And while its business is indisputably powerful, the multiples being applied to its revenues and cash flows stress the imagination. Might it grow into its IPO price? Certainly. Are there significant risks to achieving this? Absolutely.” –Forbes