I must admit that I have never liked Xmas as an abbreviation for Christmas. It just seems a bit flippant and unnecessary. In today's culture where many Christians perceive a war against Christmas, they see the use of Xmas as an attempt to secularize the season by taking Christ out of Christmas.
I must admit that I agreed with those sentiments until I actually looked into the history of the use of Xmas. Originally, Xmas was an abbreviation where the X represents the Greek letter chi, which is the first letter of Christ's name in Greek, ΧΡΙΣΤΟΣ. However, because of the modern interpretations of the letter X, many people are unaware of this and assume that this abbreviation is meant to drop Christ from Christmas.
The Greek letter Χ, or Chi, was a common abbreviation for "Christ" in past religious writings. Its usage can be traced as far back as the 4th century in Rome, and to 1021 AD in historic Anglo-Saxon manuscripts. Xmas began to be used in English starting in the 1500′s. Webster’s dictionary acknowledges that the abbreviation Xmas was in common use by the middle of the sixteenth century.
Even though we know from history that it isn't offensive to use “Merry Xmas,” do be aware that some still find it so, so use good judgment when using the abbreviation “Xmas.”
Merry Xmas every one - pronounced properly of course. :)