Metro/Touch will work well on devices designed from the ground up for this, i.e. tablets, but it will have a very slow take up on desktops. How many people actually have touch-ready monitors? A fraction of a fraction of a percent probably. Most will be controlling Metro with a mouse/keyboard, which could actually get pretty tiring very quickly. How many workarounds will come out for disabling Metro entirely on desktop PC's I wonder?
The desktop is here to stay, and considering where MS actually get most of there money from, it's highly likely that Metro will even be the second choice interface in Windows 8 Enterprise (or whatever it's called). Corporates will not tolerate an interface like Metro, and would steer clear of 8 just as they did with Vista if this was the case.
Crazily enough, it's actually apps like Media Center that would get the most benefit from Metro. It would be an ideal 10' interface for the TV, all controlled via a remote. Perfect, but MS seem to be moving away from this now, which is a complete shame.
Would there be any real benefit for dedicated HTPC's with the WMC frontend to switch to 8, when 7 does everything they need? I seriously doubt it.