The odometer has rolled over from 20091231 to 20100101. An new day, new month, new year, new decade, at least for the Gregorian calendar. Of course, it's only 20091219 on the Julian calendar, and something else on every other calendar. You can see a few of them at Calendrica. That's why integer dates were introduced, to sort through this confusion of calendars. For instance, Julian dates start from the year 4713 BCE and count days continuously. No years, months, weeks, just days. Modified Julian dates use a more recent epoch, in 1858, while truncated Julian dates count from 1968. Excel serial dates count days from 1900 CE. Unix time is finer, counting seconds from 1970.
So happy 2455197!