[TheGregmeister]

Depends whether you believe in Year 0 or not, which would make 31/12/2000 correct in the scope of the post you replied to.

Of course there was never actually a Year 0. A.D. started with year 1 A.D. of course, which means everyone celebrated the start of the new millennium and the 21st Century exactly one year early. The true and proper beginning of this new millennium and the 21st century was on 1st January 2001. For the case of the Millennium Bug, it was just the fear of computerised systems around the world malfunctioning when the first two digits of the year changed from 19 to 20, and it turned out to be a damp squib anyway!