Why celebrate Christmas? For me it is the connection to others and to the past. I focus on the giving part of the holiday, the time spent with friends, and now with the new family that's come to me through my marraige. I've slowly become more comfortable with the religous aspects of the holiday.
In my heart I honor all the of the contributing factors to the celebration of Christmas as we now know it, be they pagan, Christian or secular. I think its the last great festival we allow ourselves in the US nowadays and it's also a time to go a bit over the top. It's a way to embrace life and most of all, to me at least, to appreciate children. They are what really makes the holidays shine!
As others have said, do only what you are comfortable with. But don't let fear hold you back from trying. You might enjoy volunteering some time or funds to a local charity or cause. Giving can bring such a wonderful feeling. It's addictive, actually!
I know that the JW's scoff at this particular Christmas sentiment and say things along the lines of "bringing the truth to people all year round is more important than showering them with gifts once a year, blah, blah, blah..."
I say that if the giving is sincere than it's a good thing. I say that I'd rather see an outpouring of people trying to do the right thing once a year than them living in a joyless JW stupor 365. Just my opinion.
Christmas has helped fill up the emptiness I was left with after leaving the JW's. It's just a piece to the puzzle of what's helped me form a new life away from my upbringing, but I think it's an important one.