As with all end of the world 2012 predictions there are different views as to what the prediction or prophecy actually means. In 2000, some people thought space aliens would come to Earth and others thought it would be the second coming of Christ. As far as I remember, those examples were not unlike the other ideas of what would happen, the most accepted of which was that there would be a massive computer/ digital problem because of the date.
The same is true for proponents of Aztec calendar 2012. There are those who go way out there and claim things about the end of the world, but the truth is that it is not a prediction of the end of the world but the beginning of a new era. Those who are more credible have based their theory of a world changing event starting according to the Aztec calendar 2012 not on some programming errors but on artifacts and records from around the world.
The Aztec and other ancients around the world have put enormous importance on symbols and other records of a recurring (tens of thousands of years apart) alignment of the Earth with the Sun on a particular axis that also aligns with our galactic plane and the center of our galaxy. The symbol for this, found across many religions and cultures, is a circle with a cross or just a simple cross. Between us and the center of the galaxy is a 'dark rift', an area empty of stars and other matter, which is often depicted in artifacts and religions as the birth canal, symbolizing the birth place of the Earth and all that is around us. 21 December 2012 is the exact date of this alignment.