Back to the video... I'm probably most looking forward to the types of interaction like you see at around 1:03. One user moves an image from the tablet to the desktop in as natural of a way as I can think of.
This is really the future of device usage... multiple devices speaking to each other, allowing the user to move data and execution context from device to device. I want to be able to cut/copy something on one device and immediately paste it to another. If I start using an app on my phone and decide that a larger screen with keyboard and mouse would be more productive, I'd like to simply put my phone away and open up my computer to see the app ready for use in the state I left it on the phone.
Apple is probably leading this effort at the moment, but the "One Microsoft" strategy feels like it could really take it to the next level if done well.