I just found this on the Wikipedia entry for "List of Common Misconceptions":
http://en.wikipedia.o...common_misconceptions
From Wiki:
"Xmas" is not a secular plan to "take the Christ out of Christmas." "The usual suggestion is that 'Xmas' is ... an attempt by the ungodly to x-out Jesus and banish religion from the holiday." However, X stands for the Greek letter Chi, the starting letter of Χριστός, or "Christ" in Greek. The use of the word "Xmas" can be traced to the year 1021 when "monks in Great Britain...used the X while transcribing classical manuscripts into Old English" in place of "Christ". The Oxford English Dictionary's "first recorded use of 'Xmas' for 'Christmas' dates back to 1551."Paul Brians adds that, "so few people know this that it is probably better not to use this popular abbreviation in religious contexts."
Interesting, as many rail against it either being a secularisation of the holiday or an Americanisation... and yet, it isn't!
Of course, you all knew that already, right?