The controversial "Ribbon" user interface that Microsoft introduced in Office 2007 is being used for some of Windows 7's built-in applications, such as WordPad and Paint.

According to Mike Nash, corporate vice president of Windows product management, the Ribbon will be adopted for many other Windows 7 applications from Microsoft as well as third-party vendors.

"This is one of the things we think will differentiate apps written for Windows 7, as opposed to those for earlier versions of Windows," Nash said in an interview today, as the company released the Windows 7 beta for public download.

Microsoft's site was overrun early Friday by would-be downloaders eager to get their hands on the operating system, which Microsoft maintains will ship in early 2010, despite evidence that it will arrive before that. Site traffic was so heavy that the company later postponed the rollout, but did not specify a new date.

Part of Microsoft's overall plan to modernize its user interfaces and catch up to Apple in this key area, the Ribbon replaces the drop-down menus, icons and toolbars that have dominated applications from Microsoft and most other vendors in the past two decades.

Proponents said the Ribbon provides a quicker, more elegant way to access an ever-increasing set of commands and features.

According to Nash, the Ribbon offers a much-needed refresh to WordPad and Paint, two "applets that hadn't been touched by us since the mid-'90s."

To encourage software developers to adopt the Ribbon, Microsoft is including Ribbon development tools in the free software development kit for Windows 7, as well as in the latest version of Microsoft's .Net programming environment, he said.

But critics, and there are more than a few, said the Ribbon is rigid and requires them to relearn commands and shortcuts they were already happy with.

Windows 7 itself doesn't use the Ribbon UI, though there are a number of UI changes that may also initially alienate hardcore XP fans or less-technical users.

That could lead to the same sort of backlash that Windows Vista faced. Microsoft's task with Windows 7 is compounded, he acknowledged, because it is aiming to make Windows 7 perform equally well whether is running on a 9-in. netbook screen, a 42-in. plasma TV or in a multimonitor office environment.

A 17-year veteran of Windows development, Nash said, "this is not a new problem." He is confident that for most users, the "short-term pain of transitioning from Version X will be outweighed by the duration of the benefit after you learn Version X+1."