Thanks for sharing your experiences in designing Windows 8. The charms and the use of edges are clever. As a UX designer, I am very aware of a problem however that I should mention.
The color scheme of Windows 8 is highly problematic.
In WP7, you can set a theme color so the default apps are at least somewhat unifying the experience in the midst of a chaos of well designed and poorly designed third-party apps. In Xbox Metro, the experience is unified with a theme color (Xbox's green), while juxtaposed with colorful tiles that show TV and games. Things pop and don't seem chaotic.
In Windows 8, meanwhile, it's a crazy rainbow of colors which third-party apps will surely not be able to follow. Are there any reasoning behind why email is yellow and calender is red, and so on? They all seem arbitrary decisions to me, and are designed to only look good for the particular arrangement of tiles in the demo for now - almost any user intervention will destroy the color composition balance of the Start screen.
A good color scheme is not only for beauty, but also a unifying experience for users. I can see the understanding that the differences of W8 apps are exaggerated so it may coexist better with websites as apps - but I doubt it's a good strategy. Having a unified color scheme will help users distinguish well designed or official ones, versus ones that aren't designed for Windows 8. It will also reduce unnecessary noise in the design.