Ferrous Floatation [Ask the experts]

In this issue of IEEE Control Systems Magazine, we invite Carl Knospe to respond to a query on magnetic levitation. He answers the question 'In my control systems textbook, one of the examples of feedback control is a magnetically levitated ball. An electromagnet above the ball is used to control its position. I have also seen a lab experiment of this kind advertised for sale. Is this just a neat toy or could it be used in a practical application? Why is a control system necessary? Couldn't levitation be achieved with only permanent magnets, which would use less power? Finally, are electromagnetic systems hard to control?'