If the government wouldn't tell, it's a sure bet that someone would leak the info to the press. In which case some of us would believe it and some of us wouldn't. We'd be having this same conversation lol! At any rate, I'm not going to worry. We're all going to die some day and we should take that as incentive to live life to it's fullest.
They wouldn't tell us because we would all freak out and riot and the world would be thrown into chaos, and they wouldn't be able to Hide in their bunkers underground because it's said that the sun will get really hot and burn us alive, and the bunkers are already built just in case, but 2012 isn't going to happen.
I don't think so because if they say the world will end(it won't) people will commit suicide because they don't want to die painfully ( as in dieing slowly) and if the government gets it wrong they are responsible for thousands or even millions of suicides globally.