  We discuss the present bounds on the relativistic energy density in the
Universe parameterized in terms of the effective number of neutrinos N using
the most recent cosmological data on Cosmic Microwave Background (CMB)
temperature anisotropies and polarization, Large Scale galaxy clustering from
the Sloan Digital Sky Survey (SDSS) and 2dF, luminosity distances of type Ia
Supernovae, Lyman-alpha absorption clouds (Ly-alpha), the Baryonic Acoustic
Oscillations (BAO) detected in the Luminous Red Galaxies of the SDSS and
finally, Big Bang Nucleosynthesis (BBN) predictions for 4He and Deuterium
abundances. We find N= 5.2+2.7-2.2 from CMB and Large Scale Structure data,
while adding Ly-alpha and BAO we obtain N= 4.6+1.6-1.5 at 95 % c.l.. These
results show some tension with the standard value N=3.046 as well as with the
BBN range N= 3.1+1.4-1.2 at 95 % c.l., though the discrepancy is slightly below
the 2-sigma level. In general, considering a smaller set of data weakens the
constraints on N. We emphasize the impact of an improved upper limit (or
measurement) of the primordial value of 3He abundance in clarifying the issue
of whether the value of N at early (BBN) and more recent epochs coincide.
