Oh, that's not for Christians - it isn't about the rapture. As far as I've been able to glean, it seems that on Dec 21, 2012, the Anunaki will return to earth from the approaching planet Nibiru. They will then re-assume their role as Nephalim, dominating human kind. Toss in Xenu and you might even get some Scientologists going for that one.
The claim is that the Mayan Calendar 'predicts' the end of time on that date, or something like that. The coolest videos I've watched incorporate the "Mayan Prophecy", Nostradamus, some American Indian folk tales, geological impossibilities, extra-terrestrial invasion, and a planet that orbits on a plane perpendicular to the solar ecliptic with a 3,600 year cycle.
Sort of like the year 2000 scare. Computer memory used to be so expensive that programmers only used the the last two digits (decade and year). The fear was the world was going to come to a crashing halt when the computers stopped working.
I actually spent 3 days back-country camping with a guy who turned out to think he was going to be some sort of messiah when 2012 went all hizzy fashizzy and whatnot. I didn't know this until almost nightfall on our first day out there. Anyway, rather than kill him, I let him ramble on about all this stuff to avoid confrontation.
Friends of mine, back in the 1970's, believed that when we experienced the "Harmonic Conversion", with all the planets lining up, that central Canada was the "safest from earthquakes and floods," sold Everything they owned and moved there and.........nothing happened! We're not so much friends anymore.