you might not even notice the difference of between 2 photos, same lens, taken with the d40 and d80. The d80 however is far more capable, more features, and has the all important (for me) autofocus motor. This mean that if you buy a 50mm f1.8 for example, it will autofocus with the D80 and not the D40. Also opens up a much wider (and cheaper) range of lens.