Google (NASDAQ: GOOG) is now one of the 25 most valuable public companies in the US based on market cap. With a value of $169 billion, its market cap is now ahead of IBM (NYSE: IBM) and just behind Cisco (NASDAQ: CSCO) and Berkshire Hathaway (NYSE: BRK.A).

While the statistics are meaningless by themselves, they show that Google may be overvalued by most measures. In the last quarter, IBM had revenue of $22 billion. Google's was under $11 billion. Cisco's was $8.9 billion.

The easy argument in Google's favor is that its revenue is growing faster than it is for these other companies. While that is clearly true, it is also true that share price is to a large extent a measure of future growth rates. Search-based advertising continues to grow at a rate of approximately 50% year-over-year, but, as the absolute number gets larger, that figure is almost certain to fall off.

The other argument that appears to make Google's valuation rich is that its stock trades for $540. Its 52-week low is $368. The company was growing just as fast, if not faster, when the stock price was at its low.

So, why is Google worth so much more today?

Douglas A. McIntyre is a partner at 24/7 Wall St.