Interesting question.
I do not believe in the whole "December 2012 Mayan calendar thing." I'm not saying it definitely won't happen, but it certainly not something that worries me---Like Jesus said, only the Father knows.
I wouldn't say that Christians who believe in this "prediction" are heretics. St. Thomas Aquinas defined heresy as, 'a species of infidelity in men who, having professed the faith of Christ, corrupt its dogmas'. An example would be if a Christian were to deny the divinity of Christ.
Although, I may not hold much to the Mayan thing, I do tend to believe that there is a good chance that the end maybe near because of things I have noticed while reading about the Fatima Apparitions to three young shepherd children and the Divine Mercy Apparitions to one of my favorite Saints.
When the Blessed Virgin Mary appeared to the children at Fatima, she revealed quite a few things that have come to pass. Lucia, whom the Virgin Mary said would stay on the earth longer (the 2 others died young as the Blessed Mother foretold) became a nun and died as recently as 2005 at the age of 97. I took noticed the other night while I was reading about things she said that pertained to the Rosary and was somewhat struck by some of the first words when I read this (as for the rest of the words, not so much as I have experienced the truth of these words many times in my life, that it doesn't surprise me---in fact in makes me extremely thankful to God for it and to the Blessed Mother for her caring and powerful intercession):
"The Most Holy Virgin in these last times in which we live has given a new efficacy to the recitation of the Holy Rosary. She has given this efficacy to such an extent that there is no problem, no matter how difficult it is, whether temporal or above all, spiritual, in the personal life of each one of us, of our families, of the families of the world, or of the religious communities, or even of the life of peoples and nations that cannot be solved by the Rosary. There is no problem I tell you, no matter how difficult it is, that we cannot resolve by the prayer of the Holy Rosary."
Also, when Jesus appeared to St. Faustina, He not only told her (and ask her to spread devotion to) of His Divine Mercy, He also told her (talking about her country Poland): "From her will come forth the spark that will prepare the world for My final coming" (Diary, 1732). Many people think that Jesus might have meant Blessed Pope John-Paul II, the first Polish Pope. If this would be so, since he was our last Pope, he may have been the one that indeed played the role in preparing us for Jesus' final coming and we may indeed experience Jesus' final coming under the leadership of our present Pope, Benedict XVI. Again, only God knows. Mind you, when you do take the time to read about the Apparitions of Fatima and Divine Mercy they really do seem to be pointing to the fact that the "end" may very well be near.