Depends. I have seen a number of forums completely die because of holidays, and others thrive more. I think it just depends on how loyal the member base is already, that ends up deciding how the stats on the forum look during that time.
Where I live, there is no holiday season. People won't migrate in great numbers to holiday destinations. Yes, people go on vacation in single or as a family, but that is either in summer when it is too hot or when they feel so.
Given the most recent holiday period, I was rather bus myself! Healthcare is quite a busy time during the holiday season.
Nonetheless, like @Joshua Farrell mentioned, I've seen communities just completely die and others thrive. Depends on the area and the member base you have. I'd recommend getting contests and other activities going before the holiday season begins to get people more involved.