While Apple (AAPL) and Facebook (FB) have grabbed the headlines this year, Google's (GOOG) shares have quietly made incredible gains.

Google's stock price has risen 48% in the past year, fueled by a stabilizing search advertising business and investor enthusiasm over the company's growing wireless segment.

Google's rise helped it hit a notable milestone Monday. The company's market value briefly surpassed that of Microsoft (MSFT), making Google the world's second-largest technology company behind Apple. (Microsoft owns and publishes Top Stocks, an MSN Money site.)

The two changed places throughout the trading day Monday. Google traded up less than 1% at noon ET to $759.56, which put its market value at about $248.7 billion. Microsoft was down very slightly to $29.64, which put its market value at $248.5 billion.

Some observers linked the market action to a bigger story about the decline of the PC. "The PC hardware business is obviously struggling," Wedge Partners analyst Martin Pyykkonen told Bloomberg. "The transition here is pretty straightforward in terms of where things have moved to, and certainly that's cloud, that's Web."

The story here is Google's unrelenting innovation and ability to produce shocking amounts of cash. It should generate at least $12 billion in free cash flow this year, calculates Henry Blodget at Business Insider.

And while some observers have criticized Google's decision to basically give its Android platform away, Google has seen an amazing response from phone manufacturers. Android is the biggest software threat to the iPhone and has helped Samsung become the mobile giant it is now.

Google's ad business continues to grow. Google is likely to overtake Facebook as the No. 1 display advertising company, says the research firm eMarketer. When that happens, Google will be the top company in the three main areas of digital advertising: search, mobile and display.

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