Yes. I don't see why Atheists shouldn't celebrate Christmas. There is proof that Jesus really existed - although most likely not as the son of God, just as a really cool guy who wanted peace. I respect Jesus' views, and although I am not a Christian, I strongly agree with most of the morals in the Bible. A lot of it makes sense. Anyway, Christmas is really meer of a cultural than religious celebration now - it has now become a traditional western holiday.
I personally think that everybody should celebrate Christmas - it is the holiday that endorses peace and goodwill after all. Isn't that everyone's concern?
I'm an Atheist and I enjoy Christmas. I like spending time with my family and friends, enjoying each other's company, and doing gift exchanges. Plus Christmas is celebrated in different ways, for different reasons all around the world.
I'm an atheist and my family does, but mostly out of tradition. My parents don't believe in God, but they were both raised in strongly Christian families, so they've just continued the tradition with my little sister and I. We just don't go to Church of do the religious aspect of anything. There is still emphasis on the giving and caring part of it. Just because we're atheists doesn't mean we're bad people. Christmas is as important to culture as it is to religion. There's nothing weird about it. (: