A Jewish friend of mine sent an email out about this just the other day. She was complaining about her SIL, also a Jew, bitching about how my friend's family does celebrate Christmas, while still considering themselves very Jewish. :P Anyway, my friend said that her great-grandparents had begun celebrating the tradition of tree and gifts and a big meal on Christmas day in order to feel more American, and not because they wanted to feel less Jewish. So, to her family, Christmas is part of feeling American and participating in American holidays, and very little to do with Christianity.