OK, OK, I won't push it.  But I am one of those picky people who insist that since there was no "0" year, the new millennium really didn't begin until 2001.  Not that there's much chance that it was exactly 2000 calendar years ago that Jesus was born, what with all the miscounting, calendar fiddling, etc., through the years.  But if you have to have a number, you might as well get it right in theory, if not in practice.  

But think about it.  Once you get to, say, your late 30's or early 40's, do you really care if you get a birthday greeting a day or two early, or even a day or two late?   Aren't you just glad people care enough to remember you were born, and express their appreciation for having you as a friend or relative, so that you can enjoy sharing a little joy with them?  Surely Jesus,  2000 years (give or take) after his arrival is at least as mature and understanding as that about our remembering his birthday (ditto on the sharing life).  The point is the attitude of the heart, not the absolute accuracy of the calendar. 

I take a similar (possibly contradictory) stance on spelling and grammar, an area in which I'm blessed (or cursed) with some discernment (though you can bet I spell-checked "millennium").   If I see I've made a mistake, I try to fix it.   If I know the rule, I try to follow it (quotation marks at the end of sentences still cause me to hesitate...before the period or after?). But ultimately the point is to communicate, not to show off how much you know, so when in doubt, I shrug my shoulders and remind myself few people care about spelling and grammar these days, anyway, and forge ahead.  Occasionally I even point out errors of others, but only when I think they'd really want to know (like on websites, for example).  I'm sure even then they're rolling their eyes and using terms like "anal" (and several closely related to it), and wondering if I have a life AT ALL.  I know, I know.  I even took a college-level grammar class at UT as an ELECTIVE...for the FUN of it.  And it was, pretty much.  Hey, some people are good with cars....

My point was...or will be, now...whatever the calendar tells you, or your friends tell you, enjoy each day you're given..."Let me live as if today were all I had..."   In a very real sense, today IS all we have.  So what are you waiting for?   If you're looking for an apology for my ending a sentence with a preposition, forget it!

Mark

P.S.:   As it turns out, "millennium" seems to have two acceptable spellings.   I won't bore you by telling you what the other one is.