  Using the spectacular new high redshift supernova observations from the
HST/GOODS program and previous supernova, CMB and galaxy clustering data, we
make the most accurate measurements to date of the dark energy density rho_X as
a function of cosmic time, constraining it in a rather model-independent way,
assuming a flat universe. We find that Einstein's vanilla scenario where
rho_X(z) is constant remains consistent with these new tight constraints, and
that a Big Crunch or Big Rip is more than 50 gigayears away for a broader class
of models allowing such cataclysmic events. We discuss popular pitfalls and
hidden priors: parametrizing the equation-of-state w_X(z) assumes positive dark
energy density and no Big Crunch, and the popular parametrization w_X(z)=w_0
+w_0' z has nominally strong constraints from CMB merely because w_0' > 0
implies an unphysical exponential blow-up rho_X ~ e^{3 w_0' z}.
