Apparently, Planet X (a.k.a. Nibiru) was spotted by astronomers in the early 1980's in the outermost reaches of the Solar System.
It has been tracked by infrared observatories; seen lurking around in
the Kuiper Belt and now it is speeding right toward us and will enter
the inner Solar System
in 2012. So what does this mean to us? Well, the effects of the
approach of Planet X on our planet will be biblical, and what's more
the effects are being felt right now. Millions, even billions of people
will die, global warming will increase; earthquakes, drought, famine,
wars, social collapse, even killer solar flares
will be caused by Nibiru blasting through the core of the Solar System.
All of this will happen in 2012, and we must begin preparing for our
demise right now

As investigated in my previous article "No Doomsday in 2012",
a lot of weight had been placed on the end of an ancient Mayan
calendar, the "Long Count". According to this calendar and Mayan myth, something
is going to happen on December 21st, 2012. Now the world's Planet X
supporters seem to have calculated that this hypothetical, deadly
planet will arrive from a highly eccentric orbit to wreak gravitational
havoc on Earth, sparking geological, social, economic and environmental damage, killing a high proportion of life in 2012.

http://www.youtube.com/watch?v=SaHdUrbPME4