This is a topic I've been discussing privately since I think it is hypocritical for atheists to celebrate religious holidays.
Why should it be? Christians adapted a pre-christian festival to their own purposes. This is true about Christmas, and of course all other Christian holidays as well.
Atheists simply do the same thing. There is a public celebration going on, and we adapt the parts we like (giving gifts, lights, eating and drinking) and throw out the superstitious junk.
How is this more hypocrisy than Christians celebrating e.g. Easter, which is a Christian adaptation of Jewish, Mithraic and a number of other celebrations?
Giving old customs new meaning is not exactly a novel idea. Why should atheists be prevented from doing the same?