The end of the world in 22th, December, 2012 is so reliable as the end of the world in 31th, December 1999/1st, January, 2000.
And why is this? Because Mesoamerican Long Count Calendar ends on that day... I respect everybody´s beliefs but...please...! Give me a break...! Guys, Mesoamerican cultures existed from about 2000 BC until Spanish colonization in the 15th and 16th century! They were complex and advanced cultures, but not that advanced...
One should listen more to science...! If we do not kill each other and you can overcome climate problems and other problems in the future, we´ll have more 0.5 billion to 1 billion years of lifespan (however an asteroid impact may occur also, during this long period). At that time the Sun will simply destroy Earth´s Biosphere. 5 billion years from now our Sun will star Red-Giant phase. Mercury, Venus (and Earth, probably) will be swallowed with that phase evolution.
So, 0.5 billion to 1 billion years from now, we´ll have to make of two choices: - die here, or sail to other worlds. I´m pretty sure that at that time our Science knowledge and Technology advances will allow us to do that.
Take care.