Actually, Scientists ( Meteorologist etc ) have one very good reason for the end date;
The sun, the earth, the milkyway. There is a giant blackhole in the center of the milkyway, but on the 21st of dec 2012, there is this thing called the galactic alignment which means that the sun, earth and the center of the milkyway all line up ( galactic alignment ) and the pressure of the black hole will force the sun to explode ( to much pressure on the sun ) which will obviously destroy the earth :| Bullshiat.