Throughout history, there have been many prophecies of the End of The World Many which attempt to get specific end up being proven wrong by virtue of the world continuing to exist. Others haven't been proven yet one way or the other, because their dates haven't come yet. 2012 prophecies are among the latter group.
Offline, there have been some rumblings about 2012 prophecies, but online is where there are many mentions of this theory. Every forum seems to have at least one thread about 2012, bloggers who are willing to discuss things of this nature have jumped on it, and there are several sites about it.
So what are these 2012 prophecies- Basically, they all stem from one root fact The ancient Mayan calendar ends in 2012. This fact is believed by Mayan-prophecy adherents to signal that the entire world will end at that point; that the Mayans didn't bother to make another calendar because they figured they wouldn't need one.
Specifics of this world-ending vary depending on who is interpreting the data. Some believe the world will end with a cataclysmic natural disaster, such as a meteor strike, while others who want more believability tone it down a bit and claim that it will be "the end of the world as we know it" rather than an outright destruction of the planet itself. There is a bit of interesting science thrown in, like the fact that there is projected to be an event known as a galactic eclipse on December 12th, 2012. This is only supposed to happen every 28,600 years. 2012 prophecy believers think this may herald some major changes for the Earth.
Needless to say, skeptics abound. Even though some other Mayan prophecies seem to have been accurate, these skeptics point out several logical holes in the 2012 prophecies. Among these counterpoints are simple observations like the fact that Mayan culture may have simply ended before their scholars could put together another calendar for Dooms Day. Others say that the Mayan calendar system consisted of set periods far longer than one year, and this one just happens to end in 2012. They claim there is no special significance to this at all.
Like most nebulous prophecies, there are points and counterpoints revolving around every possibility whether for or against. The only way to know for sure, unfortunately, will be to wait until 2012 and see what actually happens.