  A generic property of the cuspy simulated virialized halos in cold dark
matter cosmogenies is that their concentration is inversely correlated with
their mass. This behavior has also been confirmed in observations, although
differences in the exact form and dispersion of this so-called
mass-concentration relationship have been reported. Some observational studies
of massive halos suggest that they are statistically over-concentrated with
respect to the expectations of Lambda-CDM. Here we investigate the impact that
various published mass-concentration relationships, both from simulations and
derived from observations, would have on other cosmological observables, in
particular considering upcoming surveys. We find that an integral measure of
lensing shear, such as counts of peaks from halos, is very sensitive to the
relationship between mass and concentration at fixed sigma-8, and the disparity
between some reported fits is much larger than the impact of uncertainty in
sigma-8 itself. We also briefly assess the impact of baryonic physics on
cluster scale observables, using state-of-the-art simulations, concluding that
it is unlikely to give rise to the high concentrations reported for some
clusters.
