  We study the effect of U=0 impurities on the superconducting and
thermodynamic properties of the attractive Hubbard model on a square lattice.
Removal of the interaction on a critical fraction of $f_{\rm crit} \approx
0.30$ of the sites results in the destruction of off-diagonal long range order
in the ground state. This critical fraction is roughly independent of filling
in the range $0.75 < \rho < 1.00$, although our data suggest that $f_{\rm
crit}$ might be somewhat larger below half-filling than at $\rho=1$. We also
find that the two peak structure in the specific heat is present at $f$ both
below and above the value which destroys long range pairing order. It is
expected that the high $T$ peak associated with local pair formation should be
robust, but apparently local pairing fluctuations are sufficient to generate a
low temperature peak.
