How Well Can Cosmological Parameters Be Estimated from CMB Observations?
  The CMB anisotropy depends sensitively upon the slope and amplitude of primordial density and gravitational wave fluctuations, the baryon density, the Hubble constant, the cosmological constant, the ionization history, {\it etc.} We report on recent work showing how well multi-scale measurements of the anisotropy power spectrum can resolve these factors. We identify a hypersurface in cosmic parameter space that can be accurately localized by observations, but along which the likelihood will hardly vary. Other cosmic observations will be needed to break this degeneracy. 
J. Richard Bond, Richard L. Davis, and Paul J. Steinhardt