Do Atheists celebrate Christmas?

Yes and no. Celebrating the birth of Christ? No. Celebrate a generic holiday around the time of the Winter Solstice? Most likely. Xmas is not just a short form for Christmas, it's also a great way to talk about the same holiday while avoiding the religious connotations. Let's have a look at why today, it's definitely more Xmas than Christmas anyway, and why people who aren't Christian can celebrate it:

Trees and decorating them: not a Christian idea. I believe it originated in Germany.

Red and green: traditional Pagan colours around the Winter Solstice. No particular significance placed on these colours around the birth of Jesus, if I remember the Gospels correctly.

Gingerbread: I don't remember reading about those in the Bible... Nor do I recall any meatballs, julmust, eggnog, candy canes or cranberry sauce and stuffed turkey, or brussel sprouts... or chocolate, for that matter. Or any other food traditionally linked with the holiday.

Father Christmas - there's an old Pagan tale of the Holly King, if I remember it correctly.

In Sweden, we also enjoy a one-hour Disney special - also not mentioned in the Bible - and we have a tradition of giving rice porridge to the helping spirit (i.e. "tomte") of the house and garden. Very little to do with religion.

Stars on the top of a tree and gifts and gold colour - yes, fair enough, that's from the tale of the Three Wise Men. But the rest? Not so much.

The Winter Solstice was a traditional time for deities to be born in various mythologies, so where better to place the birth of the Son of God? Jesus wasn't even born in December. Look at any of the traditional Pagan holidays, and you'll find a Christian holiday superimposed nearby. It was a bit of a PR stunt from the church back in the day. Instead of stopping the people from celebrating those dates, they just changed their meanings, thus making the conversion a lot easier. (They just weren't very successful in getting the Vikings to give up their Midsummer Solstice celebrations, which we celebrate to this day!)

The Nordic word for Christmas, incidentally, is "jul" - compare this with the English "Yule", it's pronounced the same way... Stubborn old Pagans, Scandinavians... ;)

So yes, I'm celebrating a holiday this time every year, albeit not the birth of Jesus, and I'm planning on continuing my Yuletide Xmas celebrations in the future without any mention of babies born in mangers in Bethlehem thousands of years ago.

P.S. Not to mention Lucia... heh. Read more at Wikipedia: St. Lucy's Day .