Gruber does mention Metro:

The lack of skeuomorphic effects and almost extreme flatness of the “modern” (née Metro) Windows 8 interface is remarkably forward-thinking. It’s meant to look best on retina-caliber displays, not the sub-retina displays it debuted on (with Windows Phone 7.x) or the typical PC displays of today. That said, I think there’s a sterility to Metro that prevents it from being endearing. It epitomizes “flat” design, but I don’t think it’s great design.