Maglev trains: why aren't we gliding home on hovering carriages?

It is lightning quick, clean, green - and expensive. But shouldn't we think again about magnetic levitation?

Clean, green, quick and quiet; no wheels, no engines to fail; able to stop quickly and safely and glide off noiselessly on a cushion of air.

Magnetic levitation (maglev) was, according to 1980s science shows such as Tomorrow's World, going to make domestic air travel defunct, humming from city to city at 500mph with negligible effects on the environment (and no need to remove your belt and shoes).