Christmas is a secular holiday
Every once in awhile, a friend, or a friend of a friend, will try and trip me up about the whole agnosticism thing, and say that I'm REALLY a Christian, I just don't know it. This normally happens when I try to do a good thing for the sake of being good, or I use a common colloquialism like "God dammit" or some such. The most recent example of this was a question on how I could celebrate Christmas, if I didn't actually believe in the birth of Christ.
My answer? Christmas is now a secular holiday.
Here's what I've done for Christmas:
Decorated a miniature plastic pine tree with lights (and put the angel I got from mom on it).
Hung pretty baubles from my ceiling
Made gifts for my friends
Have plans for making good food for a Christmas party.
The closest thing I have to "Christian" in that list is that I have an angel on the tree, but that is more because it has to do with my mom than god.
The tree, if anything, is a pagan tradition, and the rest of them are recent American traditions (look it up if you don't believe me). Santa and Frosty get more airtime and association with this holiday than Jesus does.
I'm okay with people thinking that this religion has something to do with this day (even though Jesus, if he existed, was most likely born in the summer) and that's their they thing. But for me, Christmas is about gifts, Easter is about eggs, and Lent is only good for Fat Tuesday.