Poppycock and bullwhackey! It has nothing to do with a deep understanding of the complexities of time. It has to do with the number 2000! 2000, get it? People aren't celebrating randomly based on an inner biological clock. They're celebrating because 2000 makes two millinea (sp?). But it doesn't until the end of the year that we have assigned the number 2000 to. It's a simple mathematical concept easily within the grasp of those people in charge of keeping time. Now go party. It's 2000!