As I mentioned earlier, I have a friend who licensed a single image of an apple for $10k for one year. It truly is about having photos that are good for stock purposes, as opposed to just nice photos of places and things.
Stock is a very different deal. If anyone is interested in learning the subtleties of the differences, I found reading a couple of industry magazines dedicated to stock photography very enlightening.
Of course, my photographer friend uses film - to achieve the kind of results a real publisher (as opposed to digital publisher) requires, you're looking at a $5K DSLR or a good old film camera.
[edited by: Fiver at 3:25 pm (utc) on Oct. 27, 2006]