I briefly had a D30, but an understanding dealer let me return it for the D60 when it was released. There is really nothing in terms of image quality between the two cameras - the D30 might even have a slight edge in sheer smoothness. The main advantage of the D60 is that quality is held to larger output sizes. So whereas a D30 image is limited to about 6x9 @ 300dpi, the D60 will cover a full page without interpolation.
Of course, you CAN
take a D30 image up to full page with a bit of processing, but, in general, the D60 will do the same job as a D30 but a bit bigger. Depends what your requirements are. If you don't need large prints, the D30 will let you get twice as many images on your CF card.
Colin K. Work, Pixstel