I don't beleive that the world is going to end in any way. However if it was ever going to end any time soon (which has a 99.999999999999999999999999999_% of happening) I would say it would end on 12/21/12 because of the amount of things that point to it.
But the one thing is, if the world was going to end, why not make it 12/12/12, the numbers are the same and it would just be weird. So what i mean is if I was the Myans I would say the world would end on 12/12/12 just to freak people out.
And for all we know 12/21/12 could acually be the year 122,112. This could mean 122,112 AD, or 122,112 BC. Or 122,112 years after the world or intelagent life was created and it could mean the Ice Age (however I really dought thats right, i don't know when the ice age happend) which could mean that the Myans said the world already "died" and it was just rebuildiong it self.