It's not just the lines, there's an overall workflow in the Metro UI (at least on WP7 devices) that actively reduces the number of gestures needed to get things done, at least compared to Android. Metro on a phone rocks... after 6 months with a WP7 phone, I'd rather go back to a "feature phone" than use Android again! I think Metro on a tablet will also be awesome. Metro for keyboard + mouse? I'm not sold yet.
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