Christmas is great. For a few years, I haven't really had much appreciation for the holiday. On the one hand, it celebrates one of the most important days of a religion in which I hold no faith. On the other, it is crass, materialistic, gaudy and a reflection of what is wrong with western culure. But then I realized something - Christmas is a celebration of the sum total of the component parts that make up the history of the evolution of western society, not just Christianity. The Christmas tree is a perfect example - it's actually an old pagan tradition, adopted by Christians. (Just like the holiday itself.) There is undeniably a secular side to it, representing the increasing secularism of the west. There is a fun side to it for the kids - Santa and what not. And it's pluralistic - everybody, no matter their faith or lack thereof, is entitled to a holiday on the 25th of December, unless of course they work in a job that doesn't permit such a thing.
In short, it's a holiday that unites everybody in at least some way, even if it is a superficial one. In that vein, Merry Christmas.