A New Decade?? No??

Entering the year 2010, people were greeting a happy new year, and also the start of a new decade??

So, is 2010 really the start of a new decade? Isn't our coming decade will be starting in 2011? The same thing happened way back in 2000. Y2k? Millennium? Millennial countdown? Wasn't it supposed to be on year 2001? Didn't we started our calender with year one? Or did we not? Started with year zero perhaps?

If it was year one, then a period of 10 years will bring us to year ten, and the next year, year eleven, will be the new decade. Not unless we started from year zero, then we will be celebrating a new decade recently! The same goes for the previous millennial countdown.. Please correct me if I'm wrong~

And so the question remains, did we started counting from 1 AD or 0 AD after Christ's dead?

Did I get my perceptions wrong?
what do you think?