Editor's Note: We originally published this with the wrong forward P/E and 2010 forward P/E. The error has been corrected, and we apologize for the mistake.

Knowing that my opponent's argument would likely center on Google's (NASDAQ:GOOG) current valuation, I decided to save the details of that discussion for this part of the duel.

The first common critique of Google's valuation is that the company faces unreasonable expectations, and that the law of large numbers will soon cause investors great pain. But Google is not a typical pie-in-the-sky Internet bubble company with little or no profits. It has generated $1.7 billion in free cash flow over the past four quarters, and many of its capital expenditures have been growth-related.

Analysts estimate Google's 2007 earnings per share at $11.96, which translates into a forward P/E around 33. If that seems a bit overambitious, consider that 30% growth over the next five years would place the current 2010 forward P/E just below 15. Neither of those numbers can be considered stratospheric values.

Many critics also make the flawed argument that advertising will be Google's only source of future revenues. Why should Google diversify its revenue stream now, when revenues continue to come in at a breakneck pace? It isn't a generous assumption at all to expect Google's future sales to equal half of the 2010 global online advertising market, especially when revenues from other products or services could be substantial.

I have already explained that Google has positioned itself to capitalize on many of the current trends for information retrieval. But because it isn't necessary to monetize any of those diverse projects yet, their business models can be fine-tuned, adding enhancements based on user feedback, before Google launches any commercial releases.

Just this week, it announced upgrades to Google Earth and Google Maps. The improvements were likely based on massive amounts of user-behavior data from the 100 million unique downloads of Google Earth over the past year. That's a lot of downloads for a product that hasn't contributed to the bottom line. Making that info available would be a huge selling point to potential licensees. Then there is GBuy, which may be launched as early as this month and could be just as big as PayPal is for eBay (NASDAQ:EBAY). Don't forget mobile search, Google Video, Froogle, or about a dozen others, either. While Google has yet to see a dime from most of these services, that may not be the case by 2010.

Think you're done with the Duel? You're not! Go back and read the other three arguments, and then vote for a winner.

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Foolish contributor John Bluis does not own shares in any company mentioned in this article. The Motley Fool is investors writing for investors.