HELL YEAH!

i always love this subject. and smile with the conviction that some people seem to honestly believe that the new millenium started in 2001. but if you sit down and think about it. as luvinsully has stated. the new millenium (or 3rd millenium) and 21st century started at 00:00.00 hours on jan 1st 2000. as did the 1st millenium at the same time 2000 years before. it's also correct to say that there was no year zero. as soon as the clock struck midnight at year dot, we were into year 1. but zero years had passed yet. so as soon at time actually or officially began, year 1 started.
so, if we advance almost 12 months to just before midnight 31/12/01. one year had passed. and we were about to start year two. though i doubt very much that many revellers were partying in the city centres around the world in those days. anyway, i digressed. let's cut to the chace and jump forward 1999 years to 31/12/1999. just before midnight that night, 1999 years had passed and as the clock struck midnight we were in to the 2000th year. a new millenium, a new century and a new decade.
it can be argued that a decade has not passed until 10 years have passed. hence the first decade didn't finish until the 10th year had finished, e.g. 31/12/10. that is true. but a decade is just a measurement of two points in time. such as 25/10/65 to 25/10/75. so a decade starts whenever you want it to start. so to say that a decade started at midnight 01/01/2000 and finishes at 23:59.59 31/12/2009 is correct. as it is also correct to say that the first decade ended at midnight 31/12/10.
we generally measure decades as in the 60's, 70's, 80's and 90's. but it is also true to say that 201 decades have passed since the beginning of recorded time at the end of the day 23:59.59 on 31/12/2010.

They year's go 2000-2001 is 1 year. 2001-2002 is two years. Continue this logic then 2009-2010 is 10 years, making 2010-2011 the start of a new decade.