We know that the universe is not homogeneous on small scales, and we know that such local inhomogeneities affect light propagation and hence distances which depend on angles, such as the luminosity distance. What does this mean for constraints on cosmological parameters derived from the m-z relation for type Ia supernovae? And, conversely, what does the fact that these constraints, when locally homogeneity is assumed, agree with other constraints mean for the nature of dark matter?