Hey everybody, check this out . . . A very nice little explanation, with easy-to-understand diagrams, of "flying heights," hard disk crashes, etc.
That is an interesting link, but it is a bit outdated. The newest generations of drives have the heads flying one tenth the distance quoted. The current generation flies around 10 nanometers from the disk or 0.4 millionths of an inch. To put that number in perspective, a nanometer is the equivalent of 10 atomic radii, so the current generation heads are flying around only about 50 atoms above the disk.