I think it depends on how you are getting your traffic. Conversions usually stay the course except for the actual holidays, I've found. However, I don't know if the pattern holds for something new.
Conversions aside traffic is definitely down considerably on actual holiday days, christmas and christmas dont be surprised to see 30% less traffic than normal, if not more than that. But thats just one-two days out of the month, so no reason to put it off.
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