I'm agnostic/borderline atheist and I celebrate the shit out of Christmas. I get nostalgic as hell and thjs is probably my favorite time of year. I love the music, lights, ambiance, etc. All that crap.
It doesn't really bother me that the holiday is rooted in religion, because to me, it's also very much an American tradition as well. I feel that it's so embedded in our culture that one doesn't need to be a Christian to appreciate this time of year. My family was never even remotely religious and we always celebrated when I was a kid.
IMO Christmas is what you make of it. Whether you want to celebrate the birth of Christ, give and receive gifts, take time off of work, or if you just like pretty lights, I think any reason should be enough is reason enough to enjoy this time of year.