In a few days we will reach the end of the "noughties". No doubt about that. 1980 was not part of the 1970s, for example. 1990 was not part of the 1980s. (The '60s were an aberration - depending on where you live, they started in about 1966 and ended at some point between 1974 and 1979.)
Anyway, we are seeing lists everywhere of "best of the noughties", "key events of the noughties", etc., and this is perfectly accurate. It's also accurate to talk about "best of the past decade" ... in the same sense that if we were back in, say, 1995 we could accurately talk about "best of the past decade" ... meaning the years 1986-95 inclusive. A decade is simply a period of ten years.
What we can't say, though, is "best of the first decade of the new millennium" or "best of the first decade of the new century". For better or worse, the twenty-first century and the third millennium AD (or CE) did not begin until 1 January 2001. That's because we use a calendar that goes straight from 1 BC (or BCE) to 1 AD. There is no "Year Zero" in between. Thus, the first ten years AD on the calendar don't end until the end of 10 AD. Again, the first hundred years AD don't end until the end of 100 AD. And the first thousand years don't end until the end of 1000 AD. The twentieth century began on 1 January 1901 and the twenty-first century began on 1 January 2001.
Thus, the first decade of the new century and millenium also began on 1 January 2001 ... and it still has more than a year to run.
This isn't very difficult to understand once it's explained, and it does make some difference to the world. The symbolic importance of various dates could be lost if we didn't apply the calendar correctly. Two examples are very obvious to me: first, the federation of the Commonwealth of Australia took place on 1 January 1901, and hence on the first day of the twentieth century. I'd hate to erase the date's calendar significance unnecessarily. Second, the movie and book of 2001: A Space Odyssey are set in the first (not second) year of the new millennium. There could be many other such examples, and I don't see the point of messing around with this kind of symbolism, just because the big media corporations couldn't wait an extra year to hold a grand New Millennium party ten years ago. I mean, look folks ... the concept is just not that difficult.
It's also annoying being thought of as pedantic and elitist - even somehow undemocratic - if you try to explain it. But all that said, I well recall the famous and apposite lines from William Blake:
You throw the sand against the wind
And the wind blows it back again.
Blake pretty much sums it up. So, let's agree on this much: it's the end of the noughties, whatever else it is. Sigh. Anyone want to make a list?