As I'm sure you would believe, I was taught that using the abbreviation "Xmas" for Christmas was done by non-believers to "take Christ out of Christmas". Raised Baptist - no big surprise there. But what is surprising is what I learned recently from the teacher of our catechumens class at St. George: the "X" in "Xmas" is the Greek letter Chi - the first letter of Christ's name in Greek (Xpistos, or Christos). So, no, that X isn't "X'ing out Christ's name" - it's just an abbreviation.
Also interesting, we came to this discussion of "Xmas" through a question as to why angels are frequently pictured on icons holding orbs in their hands with the letter "X" on them. Answer? The orb with an X is a sign of the authority given them by Christ. Seems simple to me.