  I discuss several issues that arise when trying to constrain the dark energy
equation of state using correlations of the integrated Sachs-Wolfe effect with
galaxy counts and lensing of the cosmic microwave background. These techniques
are complementary to others such as galaxy shear surveys, and can use data that
will already be obtained from currently planned observations. In regimes where
cosmic variance and shot noise are the dominant sources of error, constraints
could be made on the mean equation of state to within 0.33 and its first
derivative to within 1.0. Perhaps more interesting is that the determination of
dark energy parameters by these types of experiments depends strongly on the
presence or absence of perturbations in the dark energy fluid.
