I used to have a D70 and was disappointed by the sharpness of the D7000 I upgraded to after it took a bath in a river. From what I could find googling, sometime after the D70 they moved from CCD to CMOS sensors that were noticably softer on hard lines and edges.

Would love to know if anyone here knows more specifics firsthand, but that camera's sharpness has always impressed me compared to the replacements I've tried out.