Until Apple took the crown in 2010, Microsoft spent many, many years as the world's most valuable technology company. And now, for the first time ever, Google has leapfrogged its Redmond-based rival, too, taking the second place slot behind Tim Cook and Co.'s best-selling iProducts, and relegating Microsoft to the bronze medal podium. The search giant has enjoyed a strong run in recent months — share prices are up 30 percent for the quarter — and has now overtaken Microsoft's $247.27 billion market capitalization, clocking in at one point with a $248.89 billion market cap of its own. (Apple is still way out in front, with a market cap well north of $600 billion.) What accounts for Wall Street's renewed confidence in Google, which as recently as 2007 was seen as a risky investment? Here, four theories:

1. Google has a vice-like grip on search
Google controls 66 percent of the U.S. search market, says Brian Womack at Bloomberg. Microsoft, which entered the search market in 2009 with Bing, comes in at a "distant second" with 16 percent. And Google's stranglehold on search positions the company to become the biggest online display advertising company in the world. Google's global revenue from online ads is likely to hit $6 billion this year, displacing even first-place Facebook, Citigroup analyst Mark Mahaney tells Britain's Financial Times.

2. Microsoft's software business has been battered
"The PC hardware business is obviously struggling," Martin Pyykkonen, an analyst at Wedge Partners Corp., tells Bloomberg. That's bad news for Microsoft, which has long made a ton of money with its PC operating system. Although the company still gets most of its revenue from Windows and Office software, sales have slumped as more consumers turn to Android tablets or iPads to handle their home computing needs. Simply put: Customers are looking to the Cloud, not the disk drive. 

3. Microsoft has yet to prove it can go mobile
Windows 8 is set to debut later this month, and while the new operating system "is designed to be Microsoft's first to translate tidily from PCs to smartphones and tablets, Microsoft has spent years failing to prove it gets mobile," says Marcus Wohlsen at Wired. Yes, "Windows 8 looks promising, but it's hard not to picture Microsoft as an old silverback with its arms wrapped around an old Dell desktop." As for Google...

4. Android is already everywhere
The search giant is "beating its chest with the success of Android," says Wired's Wohlsen. The mobile operating system runs on more than two-thirds of the world's smartphones shipped during the second quarter. Windows Phone, on the other hand, ran on fewer than 4 percent of the devices shipped during the same period. Today, Google is more than the king of search, says Nick Wingfield at The New York Times. It took some time, but it's clearly that "Google is beginning to convince investors that it is more than a one-trick pony."