If I wish someone Happy Holidays it's because I may or may not see them for awhile. Merry Christms + Happy New Year = Happy Holidays. I do call Christmas-specific things what they are: Christmas tree. Christmas cookies, Christmas carols, etc. As long as the calendar still says "Christmas" in the little box for the 25th, that's what I'm going to call it, and all things referring to that specific holiday.

I don't get offended if someone tells me merry Christmas or Happy Holidays. Any cheerful greeting is better than none, IMO.