I would say I'm an athiest (Won't believe without proof), but I was brought up in a family that believes, but they aren't strict in it. I would believe if there was proof. Its just the way my mind works...
I celebrate it for the kindness, etc sector, of the family coming together, and the gifts as a sign of them thinking of you, etc.
Though I truely hate cards, as I believe these have no thought what so ever