As the meaning of words change, so changes what is culturally acceptable to say. When was the last time that "gay" was used the same way as in the Flintstones cartoon? (We'll have a gay old time!)
It is the same with cultural traditions.
While the origins of Christmas may be debatable, would it have been okay to celebrate with the pagans if a Christian festival was merged with a pagan one? As long as it was clear to unbelievers and brothers with weaker consciences that you did not follow pagan practices.
What about now, in the year 2011? I don't think the answer has changed. Except in place of the pagans, consider the works of the flesh that are typical of the world.
If you are honouring God in all that you do, there will be no problems with the cultural traditions in which you participate. You will be offended at the thought of ungodly compromise! If you are consistently faithful, there will be no confusion about who you serve this Christmas!
May it be a merry and God-blessed one!