Off by one errors are so much fun to debug... Celebrate whatever you want, whenever you want. Just keep in mind that in the US, the official timekeepers, NIST have said that the third millennium, 21st century and the first decade of the 21st century all official started with 2001. Of course we could just hold all our new year celebrations until Feb 3rd for Chinese New Year... Or better yet, just celebrate all over again. After all it is just an excuse to party mostly anyway right? ;)