I downloaded the application, and it prompted a restart to install a driver, but did nothing further. duet.app does nothing when I open it, and plugging in my iPad does nothing either. Looks like we have to wait for the App Store release to install the iPad half of the app.
After installing, there is an icon in my menubar that says I should open duet on my iOS [1]. I believe we wait for the iOS app tomorrow and see what's the price and how this thing works