I was raised Baha'i, but my mother has always celebrated Christmas because she never had much while growing up (her memories of the holidays involve her mother trying to commit suicide near every single year). My mother in 'holiday mode' is something to behold ...
I am quite aware of the religious aspects, and even admire it. Celebrating Life is better than death (like Easter). However, my family's been very close so, like EJ said, it's the 'family reunion' aspects I enjoy. Plus the traditions my family has are wonderful to me - getting a tree when it finally cools down, decorating the outside of the house, cooking with mom, baking treats to give to people, the yearly parade, the walking the neighborhood at night to see the displays, etc. I really loved it when I did it in Montana because the weather was more appropriate. Here in Florida, people tend to put lights on the palm trees in their yards.
Plus I just love the blingy decorations of the season. Everything just seems so much prettier.
Master doesn't celebrate Christmas (not close to his family and being a loner, plus his dad was especially drunk and abusive that time of year), so he asked if he could join my family for next Christmas (he'll have vacation time by then). I'm really looking forward to sharing my traditions with him.
(Sorry for the text wall.)