IMHO, I don't think is going to work - how are you going to support your wrist (or hand)? I don't think I can hold that in mid-air for a long time - plus how strong is the magnetic field?
I agree with the other C-Hing - just like the Tom Curise's movie Minority Report - skip the mouse and just use motion detection (similar to Wii game or XBox 360 Kinetic).
the major point is not the mouse, which is the tech. of floating, in the future this kind of
tech. will be wild wild use on many living things, really looking for it