@mike No problem with "Happy Holidays" in the right situation. I only get bothered by it when people think it is the only appropriate greeting.
For example, at Target I brought my cart full of Christmas decoration including some overtly Christian ones to the register where a member of my church was the checker. I wished them a Merry Christmas and they told me "We're not allow to say that here. I could get fired."
When people get so offended at "Merry Christmas" that they cannot even stand that greeting being exchanged between two people who are known to celebrate Christmas, then I get offended.