Happy Holidays= Peace and Goodwill
Merry Christmas = Merry Shopping
Doesn't matter to me. I someone says Merry Christmas, I will respond in kind. If I initiate it, I'll be my secular self.
Depends, if I know that they celebrate Christmas I'll say merry Christmas, if I'm not sure I'll say happy holidays.
I will never understand the "put the Christ back in christmas" people since very little if anything about Christmas is original to Christianity...
If I know they're Christian, Merry Christmas. If not, Happy Holidays. Assume nothing.