Merry Christmas! and xoxoxoBruce is correct. I think it is ignorance of the fact that 'X' stands for chi, the greek letter representing the first letter of Christ's name is what leads to Christians feeling slighted when Christmas is abbreviated to Xmas. That and the fact that it is used in a lot of commercial venues.
Personally, at work I say "Happy Holidays." Sometimes my job calls for me to have a lot more public contact, and I do this mostly out of consideration that there are other holidays celebrated by other faiths this time of year.
