  We point out that polarization measurements as planned for the upcoming
PLANCK mission can significantly enhance the accuracy of cosmic parameter
estimation compared to the temperature anisotropy spectrum alone. In order to
illustrate this, we consider a standard cosmological model and several
modifications that adjust one parameter each to fit the recently published
Maxima-1 data. While all models produce acceptable fits as far as the power
spectrum is concerned, their corresponding polarization spectra differ widely.
The strongest differences are expected for a model with delayed recombination,
reflecting the fact that polarization measurements are most sensitive to the
processes governing the epoch of recombination.
