  We investigate the effect of quenched dilution on the critical and spinodal
points in the infinite range (mean-field) and long-range (near-mean-field)
Ising model. We find that unlike the short-range Ising model, the effect of the
dilution is not simply related to the divergence of the specific heat, i.e.,
the Harris criterion. We also find the mean-field behavior differs from that of
$d=4$ (upper critical dimension) nearest neighbor model at the critical point.
These results are an important first step for understanding the effect of the
spinodal on the nucleation process as well as the properties of the metastable
state in systems of considerable interest in material science, geophysics, and
econophysics which in general have defects.
