Funny thing is, the whole baktun cycle and the end of the 13th one in 2012...it's sort of a cause for celebration. The Mayans, and by Mayans I mean the ones way back when who first made the calendar, would have loved to have been around for that. It's a rather major thing, sort of like the year 2000 for us. It would've made a great party for them, a definite cause for celebration. Party at the end of the world? Not so much...
The mesoamerican long count calendar was pretty much like an extended planner. It counts away from a specific creation date in the 3000s BCE (I can't remember exactly the approximate date). The whole system of counts, the baktun, katun, etc, was based on a creation myth of the Mayans that centered on 4 different worlds. Each one ended at the start of the 14 baktun cycle, and the next world was created. The fourth world created was the 'successful' one, where people got plunked down. So based on that alone, maybe you could see an end-of-the-world prediction. After all, if the world ended each of those times at the start of the 14th baktun, which for this cycle comes, that's right, in 2012. But that's where it changes. See, the first 3 worlds were failures, and they were meant to be ended in Mayan mythology. The fourth world, as said above, this one, with people, is the success, the one that the gods liked enough to stick people, their servants and creations, into.
And this leads back to the whole party. To reach the 14 baktun for the Mayans would be proof that the god's clearly loved them. It was also their way of showing the gods "Hey guys, check it out, it worked!" It's the end of the cycle, and the blessing of the gods.
Oh yeh, and the Mayans? They never heard of Planet X.
Anyhow, the mythos of the mesoamerican civilizations is actually really fascinating; that tiny summary up there doesn't do it justice. It used to be a little obsession of mine, actually.
Oh, and bump, I guess. Couldn't help it!
Cadalancea

"He who lives by the sword shall die by my knife. That's prophecy, if you like."