From an entropy argument it is concluded that the CMB neutrino temperature is (4/11)1/3 of the CMB photon temperature. This assumes massless neutrinos. Although neutrino contribution to the present energy density is therefore very small, it was significant must earlier, such as at the time of the Last Scattering Surface. How reliable is this conclusion? Is there a different analysis that would yield a different result, so that for example 7Li nucleosynthesis might be reconciled (although I'm not sure that there is an adjustment of the neutrino density that could fix the Li problem)?