Ah, the perennial — or whatever word indicates "every decade" — debate about when the decade ends. Do you count 1-10, or 0-9?
Why not do both?
In Mesoamerican calendrical systems, there’s an interesting tendency to lap the edges of things. The last day of a month is also the "seating" of the next; the five leftover days in the solar calendar are the seating of the following year. So it seems to me that we can resolve this entire problem by agreeing that any given 0 year is the end of one decade (going by the math) and the seating of the next (going by the social construct).
Happy 2010, people, the end of the aughts and the seating of the upcoming teens. May it be better than what came before.