Update 1: I see Avatar has already earned $287 million dollar worldwide in opening weekend! Looks like my predictions are getting closer to realization. Let's see.
Update 2: As of today,Avatar cross 726 million US dollar in worldwide gross revenue! Looks like my prediction of crossing 1 billion dollar (even before it released) is going to be correct!! Check - http://en.wikipedia.org/wiki/Avatar_(2009_film)
Update 3: Here you go from wikipedia on Avatar crossing the billion dollar mark as per my prediction - After 17 days of being released, Avatar has come to gross $352,111,000 in the United States and Canada and $666,700,000 in other territories with a worldwide total of $1,018,811,000, making it the fastest film to hit the $1 billion mark.This now makes the film the fourth highest grossing of all time unadjusted for inflation.
Update 4: Last might I saw it second tome in Regal Dublin 3D IMAX with Sumit Bhai, Shahriar. And by now it crossed 1.6 billion dollar gross earnings worldwide. Here is the link for James Cameron's original script of Avatar that he wrote in 1994.
Update 5: After 45 days of domestic release, Avatar has grossed over $594 million, and $1.444 billion in other territories after 47 days of international release, for a worldwide total of $2,039,222,000 .On January 25, 2010, after only 41 days after its initial release, it surpassed Titanic's worldwide gross to become the highest-grossing film of all time worldwide.On January 31, 2010, it became the first film to earn over $2 billion.