X-mas is perfectly legit. No more reason to panic because, "They're taking the Christ out of Christmas!" ...because they're not. X is a symbol for "chi" in Greek. (How did I forget that from my college years and my desire to be in a Greek sorority??)
I learned that tidbit of information the other day from a friend who is in seminary. But since you don't have access to her, here is an abbreviated version through Wikipedia:
Usage of X for Christ in ancient languages
The word "Christ" and its compounds, including "Christmas", have been abbreviated in English for at least the past 1,000 years, long before the modern "Xmas" was commonly used. "Christ" was often written as "XP" or "Xt"; there are references in the Anglo-Saxon Chronicle as far back as AD 1021. This X and P arose as the uppercase forms of the Greek letters χ and ρ used in ancient abbreviations for Χριστος (Greek for "Christ"), and are still widely seen in many Eastern Orthodox icons depicting Jesus Christ. The labarum, an amalgamation of the two Greek letters rendered as ☧, is a symbol often used to represent Christ in Catholic, Protestant, and Orthodox Christian Churches.
The occasionally held belief that the "X" represents the cross on which Christ was crucified also has no basis in fact. Saint Andrew's Cross is X-shaped, but Christ's cross was probably shaped like a T or a †. Indeed, X-as-chi was associated with Christ long before X-as-cross could be, since the cross as a Christian symbol developed later. (The Greek letter Chi Χ stood for "Christ" in the ancient Greek acrostic ΙΧΘΥΣ ichthys.) While some see the spelling of Christmas as Xmas a threat, others see it as a way to honor the martyrs. The use of X as an abbreviation for "cross" in modern abbreviated writing (e.g. "King's X" for "King's Cross") may have reinforced this assumption.
In ancient Christian art, χ and χρ are abbreviations for Christ's name. In many manuscripts of the New Testament and icons, X is an abbreviation for Christos, as is XC (the first and last letters in Greek, using the lunate sigma); compare IC for Jesus in Greek.
So, no more panic. When someone texts, writes, or says, "Merry Xmas!" be reassured that people over the years have not left Christ out of it. They simply had a broader base of knowledge than we do now. And now you know what they knew all along. In our day of 140 character texts and tweets, this is great news!
Merry Xmas everyone!