The new Nikon D5000 fits in between the Nikon D40 and Nikon D90 in terms of weight.
It’s too bad that the D5000 is now closer to the D90 in terms of dimensions, as many had wanted a more feature-packed D40, but in a D40-like package as far as dimensions and weight are concerned.
The following figures have been extracted from DPReview.
Weight (including batteries)
Nikon D40: 522 g (18.4 oz)
Nikon D5000: 590 g (20.8 oz)
Nikon D90: 703 g (24.8 oz)
Dimensions
Nikon D40: 124 x 94 x 64 mm (4.9 x 3.7 x 2.5 in)
Nikon D5000: 127 x 104 x 80 mm (5 x 4.1 x 3.2 in)
Nikon D90: 132 x 103 x 77 mm (5.2 x 4.1 x 3 in)