  We have investigated point contacts between a superconductor (Nb, AuIn2) and
a normal metal (ferromagnetic Co, non-magnetic Cu). The observed
Andreev-reflection spectra were analyzed using the modified BTK theory
including spin-polarization effects. This resulted in a polarization of Co that
agrees with observations by others, but lifetime effects describe the spectra
equally well. On the other hand, the spectra with non-magnetic Cu can be well
described using the spin-polarization model. The ambiguity between polarization
and lifetime interpretation poses a dilemma which can be resolved by
considering the normal reflection at those interfaces due to Fermi surface
mismatch. Our data suggest that Andreev reflection at Nb - Co contacts does
deliver the true magnetic polarization of Co only when lifetime effects and the
above mentioned intrinsic normal reflection are included.
