Last summer while I was an intern at MSR, I was thinking about this concept. When people are discussing face-to-face, speech is enriched with gestures (more so if you are Italian 🙂 ). Sometimes it happens that gestures depict the physical/geometrical arrangements of the objects being referenced in the discourse.
When this happens, hands moves across a sort of transparent whiteboard hypothetically placed between the speakers. I call this an “airboard”, a communication device that share some feature of a real display. For instance, invisible items can be grabbed from their position in the airboard and moved on other positions or that can be “erased” wiping the hand over the invisible item.
A pretty cool project would be to make these airboards appear with an Augmented Reality technique.