The tile-based Metro user interface that runs on Windows Phones will soon be the look and feel of all devices in Microsoft’s ecosystem. Is this smart streamlining or a foolish consistency?

At its Worldwide Partner Conference last week, Microsoft strongly implied that the Metro user interface that adorns its Windows Phones will become the standard design across the PC, phone and Xbox 360 when Windows 8 arrives.

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Microsoft did not formally announced this as such, but showed an image at WPC 2011 (below) that has the tile-friendly Metro design plastered on a laptop, a tablet, a smartphone and on an HD television via Xbox 360.

At WPC, CEO Steve Ballmer referred to the image above and alluded to Metro as the new face of Windows.

“We’re moving in a great direction in terms of a common and coherent design language and user interface across phone, slate, PC and TV.”

This was not surprising, as Microsoft has already displayed the Metro UI within Windows 8 at All Things Digital’s D9 conference in late May. But it was almost startling to see the myriad Metro-based devices together in one image. <i>Windows is soon going to look … different.</i>

As for the Metro design itself, it grows on you. Aesthetically, the tile-based look is not going to win any awards, but it does organize lots of information simply and efficiently.

Nevertheless, it’s still a bold move for the software giant in that Metro will be a different interface experience for traditional Windows PC users. In addition, even though Metro has been somewhat successful as a small-screen UI on Windows Phone 7, it has no history as a big-screen PC interface design. Users will be able to opt out of Metro and run a traditional desktop interface with Windows 8, but Metro on a PC will introduce confusion.

ZDNet blogger Adrian Kingsley-Hughes had these strong words for Metro in a blog post: “Shoving the same UI on devices that are used in different ways is either lazy or hubristic … and it disturbs me.”

You could argue that Microsoft is fixing something that isn’t broken. But although the Windows 7 PC experience is not broken, the rapidly approaching post-PC era will demand that the Windows experience be more fluid and flexible. And right now, Windows is fragmented.

Currently, Microsoft has: successful client OS Windows 7 running on traditional PCs and netbooks, a struggling Windows Phone with a completely different UI than Windows 7, and no tablets to speak of other than “Windows 7 tablets”, which run about as smoothly as a broken-down lawnmower. So Microsoft will surely need streamlined branding and a consistent look and feel as Windows expands outside of the traditional PC.

Sure, it’s a risk to trust an unproven small-screen UI as the one size that fits all. But as PC sales continue to dwindle, Windows needs to be seen as one OS that floats around every device. A common interface will help create that important perception.

What do you think of the Metro UI as the new face of Windows? Love it or hate it?