Just as a reminder, this interface is inspired by the big, clean and readable signs the authors encountered at metro stations, airports, and other transportation facilities, hence the moniker.
Windows 8 is also said to have WP7's live tiles in its tablet interface version, named "Mosh". The interface for the basic version of Windows 8, that will probably run on said slates, is dubbed "Aero Lite", and it also has other flat elements of the Metro UI. They've been dug out of the system files, and are pictured here below.
Hey, these arrows totally look like Windows Phone 7, don't they? Which, in turn, look very much like that arrow pointing to the baggage claim area from the collage Microsoft made to illustrate its inspiration for the Metro UI.
Windows 8 Aero Lite resources, borrowed from the Metro UI
Transportation signage that inspired Metro UI
We already wrote that Windows 8 will most probably appear on tablets first, maybe as soon as the holidays, and it will have a scalable interface, which adapts depending on what device it's running. For touchscreens the big live tiles of Windows Phone 7 certainly seem like a svelte idea, whereas the default Windows 8 UI is expected to be 3D and heavily customizable, although no leaks have been outed so far on this one.
source: WinRumors & WMPowerUser