I simply find that christian holidays are good excuses to get off work, see the family, eat some good food, and have fun. I don't think that celebrating the Holiday means you're practicing Christianity, it just all depends on what you feel or think during the holiday. If you celebrate Christmas and praise Jesus Christ and sing the Biblical songs, then yes, you are some-what practicing Christianity but that still doesn't mean you are exactly. If you sing the songs or praise the bible on the holiday but don't exactly accept, believe, or practice what you're preaching it doesn't mean that you're taking part in Christianity. You aren't necessarily being honest with yourself, but you also aren't taking part.
Now, if you preach the bible and Jesus on Christmas (I'll continue with that example) and you believe it, accept it, or practice it then yes, you are taking part in Christianity.
I just use it as an excuse to get free stuff, food, and to see my family.