See, that's where some of you are missing the point. It's not an offensive term, it's just not applicable. I live in a Jewish neighborhood and it wouldn't make sense for me to wave at my next door neighbor and yell Merry Christmas. He wouldn't be offended, but I'd completely wiff on my goal of spreading holiday cheer.
As a Christian I can apprciate people that celebrate other holidays. I have no problem with Happy Holidays, Season's Greetings, or Merry Christmas depending on the setting. To see it any other way, in my opinion, is just trying to start problems.