Gizmodo breaks the story of Microsoft killing the Courier Tablet project, then Microsoft’s VP of Communications confirms it:
At any given time, we’re looking at new ideas, investigating, testing, incubating them. It’s in our DNA to develop new form factors and natural user interfaces to foster productivity and creativity. The Courier project is an example of this type of effort. It will be evaluated for use in future offerings, but we have no plans to build such a device at this time.