CAMB and CMBFAST by default use 3.04 effective neutrinos (to account for QED effects etc in the early universe). The most recent paper I'm aware of astro-ph/0111408 gets something very close to this value.
The WMAP 3-year paper however, astro-ph/0603449 table 10, seems to be using 3.02 or 3.022. Of course this makes no difference at all to the results, but why this value?
Effective number of neutrinos
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Antony Lewis
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Kazuhide Ichikawa
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Effective number of neutrinos
They seem to adopt 3.022 from astro-ph/9712199, but this paper is criticized by hep-ph/9805467.
I think 3.04 is correct but I don't know why WMAP team used 3.022.
I think 3.04 is correct but I don't know why WMAP team used 3.022.