As mentioned the 21st Dec 2012 is the dates the Mayan calander predicts. This is the date that they also predict the other planet in our Solar System, recently discovered, but known by the Sumerians as Nibiru will re-enter our solar system on its orbit. it will not cause a black hole, but I believe it will cause the Earth to flp on its axis, and cause the magnetic field of the earth to change, causing devastating floods. Like the Great Flood mentioned in all ancient texts.
Nostradamus predicted this date as a Red Army sweeping from the East. Interstingly the Planet nibiru is depicted as a red planet, and its approach will be signalled from the East. I plan being in the Alps when this occurs, avoid any possibility of it being true.