That's where I wonder how well received this new interface will be. I wonder if this shell will just become something that most people skip past to get to the familiar Windows desktop. Granted, my experience as a power user (read: I'm a developer writing code and using the terminal--not on Windows but on OS X or Linux) is vastly different from that of a normal consumer, but I still think there is a common ground of using the computer to create rather than purely for consumption.
Still, very interesting concept. I'm definitely looking forward to seeing this released.
But I could see this having a different fate if it doesn't feel like a drag on the system and it can be made useful (as I think external developers will make it.)
For instance, the device used in the demo (assuming it has no other mode of operation) seems to me that it would be a nightmare for using Excel.
edit: added the last sentence.
For example, imagine a version of Excel that you could do the sum of a set of numbers by speaking "sum up these numbers" and swiping your fingers over the set that you wanted to do the sum on. Excel as it exists today may not be the best user of touch but tomorrow's Excel may provide much smarter ways of getting better milage out of it. It truly will be dependent on how well MS developers can imagine.
This gives the video the feel of a Courier-like demo. Inspirational to look at, but not realizable in practice.