I'd separate two things:
There is this belief around 2012 that has been around for quite a while in esoteric circles (though the "scenarios" differ a lot). It is up to everybody to decide for himself if he wants to believe that.
And then there is the new fad of monetizing it, which I have seen for the first time connected to the movie.
Erin wrote a blog post on this a year ago after being asked repeatedly:
2012 and the End of the World
There are also other threads on 2012 on this forum.