  We study how parameter error forecasts for tomographic cosmic shear
observations are affected by sky coverage, density of source galaxies,
inclusion of CMB experiments, simultaneou fitting of non--dark energy
parameters, and the parametrization of the history of the dark energy
equation-of-state parameter w(z). We find tomographic shear-shear power spectra
on large angular scales (l<1000) inferred from all-sky observations, in
combination with Planck, can achieve sigma(w0)=0.06 and sigma(wa)=0.09 assuming
the equation-of-state parameter is given by w(z)=w0+wa(1-a(z)) and that nine
other matter content and primordial power spectrum parameters are
simultaneously fit. Taking parameters other than w0, wa and Omegam to be
completely fixed by the CMB we find errors on w0 and wa that are only 10% and
30% better respectively, justifying this common simplifying assumption. We also
study `dark energy tomography': reconstuction of w(z) assumed to be constant
within each of five independent redshift bins. With smaller-scale information
included by use of the Jain & Taylor ratio statistic we find sigma(wi)<0.1 for
all five redshift bins and sigma(wi)<0.02 for both bins at z<0.8. Finally,
addition of cosmic shear can also reduce errors on quantities already
determined well by the CMB. We find the sum of neutrino masses can be
determined to +-0.013eV and that the primordial power specrum power-law index,
ns, as well as dns/dlnk, can be determined more than a factor of two better
than by Planck alone. These improvements may be highly valuable since the lower
bound on the sum of neutrino masses is 0.06eV as inferred from atmospheric
neutrino oscillations, and slow-roll models of inflation predict non-zero
dns/dlnk at the forecasted error levels when |n_S-1|>0.04.
