I think the U.S. government knows something about the UFO matter they're NOT disclosing. I think they know the UFOs witnessed are likely drone machines, left thousands of years ago by visiting ETs that serve to monitor the progress of both Earth and humankind---and are sending report transmissions to wherever and whomever awaits their findings.
It's suspected the U.S. has found devices that may serve to send contact to those entities who once visited Earth....but to this day, all diligent efforts to turn the machine on and establish contact has failed. And quite simply, the "visitors" are waiting for us simpleton humans to figure out the contact key code to activate the machine and contact them.
It's also a likely logical given the U.S. government assumes other "super power" countries may also have discovered similar such devices left by these "visitors"; their efforts to date have also failed, evidently.
So it's sort of a race between super power countries: Who figures out HOW to work the machine?
Had we or any other country established such contact---trust me, THAT country would in no time, dominate the entire planet with the new found whiz bang advanced weapons technology; in essence, the cat would THEN be pretty much out of the bag. MIGHT be a clue that Earth's "visitors" thousands of years ago, realized this---explains a lot.
As for December 22, 2012: The Mayan Calendar currently in existence will "reset" itself, primed to go again for another 1,500 years. It's contended by world archaeologists there is ANOTHER Mayan calendar yet to be discovered, that picks up where the current one leaves off.
No global end to civilization as we know it: No need to celebrate Christmas 2012 early; December 23, 2012 will simply be another day.