Today is Friday the 13th, the first of three this year1. It’s also 12345678902, that is the number of seconds since midnight on New Years 1970 not counting leap seconds, known as Unix time, the internal reckoning of my MacBook (date -r 1234567890) and various Ubuntu boxes. Try this:
perl -e 'print "\n",scalar localtime(1234567890),"\n\n";'
Excel counts days from the beginning of the 20th century, but Windows and Mac versions use different starting points. See for yourself by comparing PC's and Macs by typing: =DATEVALUE("1-Jan-1904"). Astronomers count Julian days from 4713 BCE, but start at noon UT on the first day of the year. Here, 1234567890 = JD 2454876.27188.
Clearly there are many ways to keep time and mark a calendar. Civilizations come and go along with their calendars: someone's, somewhere is rolling over or reaching some magic number all the time. So it is difficult to get too worked up over the Mayan calendar that will roll over in 2012, on 21 December. There is no need to worry, really there isn't.
1The others are in March and November
2Exactly so at: 6:31:30 pm EST