Steven Sinofsky and the "PDC Laptop," as seen on a webcast from Microsoft's Professional Developers Conference.

In the absence of any big news during his keynote address this morning, Microsoft Windows President Steven Sinofsky took a page from Oprah's playbook and stirred the crowd to life with the surprise announcement that all of the paying attendees at the company's big Professional Developers Conference in Los Angeles would get a free laptop.

Sinofsky said the laptop was custom-designed by the Windows team, working with PC maker Acer to create a machine that represented the best overall experience it could create with the new Windows 7 operating system. It's meant for software developers to fully explore the possibilities of the new operating system.

"We're going to take this laptop, and it's going to be available to you," Sinofsky told the crowd. "For free."

As heard on the webcast, there were huge cheers in the giant keynote hall at the Los Angeles Convention Center. Sinofsky encouraged them to stick around for the rest of the talk, recalling an incident a few years ago, when Microsoft similarly gave away a free mobile device that caused people to rush for the distribution center.

Microsoft historically has focused on operating systems and applications software, not PC hardware, but the company has increasingly been working more closely with PC makers to get them to tune their systems more carefully to work more smoothly with Windows. In that way the Windows team's work with Acer on the custom "PDC Laptop" is an interesting development even if it won't be available outside the show.

Update: In other PDC news, Microsoft this morning announced the public availability of the Office 2010 beta and the beta of Silverlight 4, the next version of its interactive technology. Both are due out in final form next year.

Office exec Kurt DelBene, acknowledging the tough act he was following, joked around with attendees by apologizing for not having any hardware to give away.