In article , not@thisaddress
says...

http://www.metacafe.com/watch/55826/..._explain_this/


It is just a demonstration of the Meisner effect for a superconducting
material. In fact, if the pictured apparatus had the superconducting material
(the black cube) attached to the dish that holds the liquid nitrogen, the
entire thing could be tipped on its side and the rotating magnet would still
hover directly over the cube, it would not slide out of the magnetic field.
That's way more impressive than just floating.

Dennis