Bas de Meijer, of the Dutch photolog Roodpetje, has some interesting thoughts about amateur photography. I hope he doesn't mind if I [attempt to] translate his post here:
"The term amateur photography is often seen as negative and associated with low quality photography. Free-photographer might be a better term. The point is that an amateur photographer isn't making a living from what he photographs. There is less pressure and you are free to shoot what you please. And that doesn't always have to be the standard model work or trusted cityscape. Check out Willem Wernsen, he shoots beautiful documentary photography. Many a professional photographer could look to him as an example of how their work should be. Pascal van Heesch treads in a area less known to amateurs; photojournalism. These are good black and white photographs and because his income is not dependant on what he shoots, he is free in his viewpoints. Selling the photos isn't the point of his shoots. And this sometimes produces extraordinary photography. The series Howrah station and HKK=HKD, in particular, stands out because of a different point of view. And he may do that more often."