The Metro UI's spare, open look is optimal for widgets. Microsoft says more complex apps such as Office and Photoshop that make extensive use of floating panels, menu items, and ribbon bars should use such Windows 7-style UI elements instead. You can think of Metro as the overlay UI, with the Windows 7 UI lurking underneath for use when needed on Intel x86-based devices.

What's unclear is how this will work on Intel x86-based tablets, where the highly dense Windows 7 interface is not likely to be easily interactive via touch. Microsoft's own gesture gurus, for example, recommend that objects be between 7mm and 11mm in size, plus 2mm of space for effective touch usage (7mm results in a miss 1 percent of the time, whereas 11mm results in a miss 0.01 percent of the time). That limits the number of buttons to between 16 and 24 horizontally -- a fraction of what many apps now display. (ARM-based devices can't run legacy Windows apps, so they'll have only Metro-style apps to worry about.)