SecondMarket, an exchange that lets private investors trade shares of privately held companies, revealed a short history of LinkedIn's (NYSE: LNKD) share price after this morning's monster initial public offering. The IPO was priced at $45, but shares soon traded at more than twice that amount, peaking at $122.

How's that compare to LinkedIn's value over the past year? See for yourself:

Editorial

Source: SecondMarket. April 2011 share price extrapolated from previous month.

At $122 a share, LinkedIn trades at about 25 times forward revenue, and some ungodly multiple of earnings. How crazy is that? Really, really crazy. Best advice: Keep your distance.

Then again, investors had similar feelings toward Baidu (Nasdaq: BIDU) and Google (Nasdaq: GOOG) after they IPO'd. Both have since been massive successes, minting money for shareholders after what seemed like insane early valuations. After Google's IPO, the New York Times warned:

After a series of missteps, Google finally pulled off its much-hyped initial public offering yesterday. The good news about this unusual I.P.O., which sought to deprive Wall Street banks of full control over the sale, is that it made it easier for individual investors to buy the stock. Of course, that may also be the bad news. At its closing price of just above $100 yesterday, Google is valued at a bubbly $27 billion.

Google is now worth $170 billion, and plenty think it's still a bargain.

What do you think about LinkedIn's IPO?