It's all very inspired by the success of the iPad, itself a radical rethink on the old Macintosh user interface. Apple doesn't officially support the iPad with a mouse, although at the recent American Telemedicine Conference, I saw a variety of iPads paired with third-party keyboards and even a few mice to recreate that PC experience.
Metro still retains the mouse when running on desktops, but it's the "Windows 8" name that will cause healthcare (and many users in general) the most grief. As of last Saturday, purchasers of systems with the current Windows 7 installed are eligible to upgrade to Windows 8 for less than $15.
Generally these upgrades are a headache for all of IT. It's usually better to start with a fresh system. I wish Microsoft would dispense with the whole idea of upgrading from one OS to another. There's a history of bad experiences.
However you get Windows 8, if you're used to the Windows you know and love/hate, you're in for a disruptive transition. Windows 8 removes the "start" button in the lower-left corner, replacing it with a Charm Bar that's invisible until you drag your pointer via mouse or touch to the top or bottom of the screen (or press Control-C if you're a real geek).