OK, while everyone gets their panties in an uproar I would just like to add my support for the phrase.
I'm not Christian. I'm not even close.
But Christmas isn't about just Christianity anymore than it is just about shopping.
It's a season and a time for remembering family and loved ones that far predates Christ. It was originally a Roman holiday where people would lay out food on their tables and then go around to all their freinds and family members homes and eat a little bit fo teh food they left out and leave a small gift.

To some the phrase is meaningless, to others it has great meaning.

Personally I like it a lot better than have a happy holiday. I don't care if I am greeted with Merry Christmas or Happy Hanukah, it just seems more personal to me and less generic or "politically correct".

People need to get off the high horse of political correctness and start remembering basic values don't come from a religion, they come from people and traditions.