Bill Gates has left the building.

It's a huge milestone for Microsoft - and the Northwest tech industry. The driving force behind the world's largest software company walked away on Friday, leaving day-to-day operations of the company he dropped out of Harvard to co-found in the hands of CEO Steve Ballmer. Gates' new focus will be working with his wife, Melinda, at their charity.

His legacy? Taking a teenaged interest in software code and creating an operating system that runs 90 percent of the world's computers. He had more than his share of misses - Microsoft has been trying to buy Yahoo! because Gates didn't foresee the impact of the Internet - but no one has done more to reshape the world of business than Gates.

That's not to mention what he and his company have meant to this rain-soaked corner of the world. Before Microsoft, Puget Sound's economy was based on airplanes, logs and fish; its culture was blue collar, and its corporate style conservative. Today, as tech blogger Wade Roush notes, you could "spend a year simply chronicling the array of Pacific Northwest startups led by executives who cut their teeth (or made their first fortunes)" at Microsoft and the tech giants that followed, Amazon.com and RealNetworks.

In addition, there are the companies that Roush calls "the Microsoft Aura," companies like Corbis, and Intellectual Ventures, Paul Allen's Vulcan companies - and even the Gates Foundation itself - which were founded with Microsoft profits and have created their own styles of innovation in different arenas. "These aren't Microsoft spinoffs exactly," Roush says, "but they are definitely part of the software giant's legacy, and are an indispensable part of the Seattle area's economy and culture."

The huge influx of Microsoft millions created a venture capital pool that's financing a whole new culture of start-ups, where serial entrepreneurs seek new opportunities to exercise their talents. Their urge to do good with their millions - and do better for themselves - could be fueling the next big things, the convergence of the digital and health sciences, or maybe a green tech revolution.

And having a second world-leading company (along with Boeing) vaulted Seattle into a new realm in the global pecking order - a transition that hasn't been easy, or necessarily welcomed, yet still is real.

So what's next for Microsoft itself? Even with Gates staying on the board as its chairman, significant change is ahead, says Mary Jo Foley, the author of Microsoft 2.0.

"Microsoft has operated well during much of its 33-year history as a partnership between the dynamic duo: The tech-focused Gates and the sales-focused Ballmer," she wrote last week. "Now that it's going to be Ballmer alone running the show, some of the more tech-focused Microsoft developers (known internally as 'Bill's Guys') and products that Gates championed could end up falling by the wayside."

But Ballmer himself says the company needs to strike a balance between giving operating divisions room to breathe while still maintaining corporate cohesion. "We're not a conglomerate, but we're not a monolithic operating company," he says. That could mean changes in the corporate structure.

Microsoft software isn't always the best. But Gates' real genius was in realizing the value of network effects, and creating a suite of office products that can work together on one platform. That, says the New York Times, was the essential difference in the paths of Microsoft and Apple: Apple focused on making outstanding products alone, while Microsoft nurtured a growing ecosystem of outside software developers who use, and are dependent on, Microsoft's technology.