It's just the best piece of glass you can buy, with an awesome framework/UI/store behind it.
To me, there are obvious verticals (medical) that this will shine in, but the best is education. I seem to have an obsession with Neal Stephenson's ideas, but this seems to get quite close (perhaps minus some obvious nano-tech related features) to the Primer from his book, The Diamond Age or, A Young Lady's Illustrated Primer. The level of engagement educational material designed with this in mind could achieve is transformative.
Beyond the verticals, this is the computer that most people should own. It takes the iPhone UI, the first successful break from WIMP (Windows, Icon, Mouse, Pointer), and scales it up to something more general purpose.
It's not perfect. I agree with two of the issues Jeff Croft mentioned - front facing camera and multi-user. But both of these are hard solutions to tackle. How do you deal with varying angles when trying to use a webcam in your lap, holding it up to your face, or propping it up on a table? How do you deal with multiple identities: syncing, switching, data storage?
Will we get one? Yes.