20 Whatever

Marty McFly: Where are we? When are we?
Doc: We're descending towards Hill Valley, California, at 4:29 pm, on Wednesday, October 21st, Twenty Fifteen.
Marty McFly: Two Thousand And Fifteen? You mean we're in the future?
Jennifer: Future? Marty, what do you mean? How can we be in the future?
Marty McFly: Uh Jennifer, I don't know how to tell you this, but... you're in a time machine.
Jennifer: And this is the year 'Two Thousand And Fifteen'?
Doc: October 21st, Two Thousand And Fifteen to be precise.

Above is an excerpt of dialogue from the motion picture, Back To The Future Part II.
You can note that the Doc character first presents the information about that future year as Twenty Fifteen, until the Marty and Jennifer characters say it as Two Thousand And Fifteen.

I remember a very rainy day back in 1997. It was a violent downpour of a storm. The type of rain that feels like it can penetrate through you. A few friends were over my place and I pondered what will we call the next decade? "This is the Nineties and the decades past were the Eighties and Seventies and so forth. Will we call it the Two Thousands, The Zeroes...?"
Someone asked why I would consider The Zeroes and I said I was thinking of place value.
Even now in 2007 there hasn't been any defined term for the decade and more importantly a smooth way of saying each year. If you ask any English speaking person what year it is, who doesn't wear tin foil and talk to their self without a BlueTooth headset, they'll tell you it's Two Thousand Seven or Two Thousand And Seven. No one will tell you it's Twenty Seven or Twenty and Seven.
Perhaps we do this from what we have heard long before the 21st century. In 1968, Stanley Kubrick's imagined 2001 : A Space Odyssey was pronounced Two Thousand and One. There was a segment on Late Night With Conan O'Brien called "In The Year Two Thousand." The huge Y2K scare in the late Nineties had many concerned if all the computers in the world could adjust to the year Two Thousand.
So will the Two Thousand prefix remain the standard? Some linguists disagree.
They believe that most of the time how we say things comes from rhythm and not logic.
Some linguists believe that we will affix the Twenty sometime in the year 2011. Simply because it is easier to say Twenty Eleven than Two Thousand Eleven. And why not in 2010? Twenty Ten or Two Thousand And Ten, which flows better?