When first seeing the sign for King Edward Hotel, the "O" and "T" lights are out. "O" is number 15, and "T" is 20. 1+5=6 divided by 2 (The number of blacked out letters) equals 3, 3+20=23. However by the end of the movie, the all letters are fully lit.
Sparrow writes his book in King Edward Hotel. On the sign, the letters "OT" are flashing. Adding these together adds up to 35. "King" (K+I+N+G) = 41, and "EDWARD" (E+D+W+A+R+D) =55. Adding these numbers individually (3+5+4+1+5+5) = 23.
A segment in the opening credits states that the Mayans believed the world would end on December 23, 2012, while in the film, Danny Huston's character reads that the Mayans believed that the world would end on December 12, 2012. In actuality, the Mayans did not believe the world would end in December 2012; they believed a new world would be created. (The date of this is still widely disputed as well, with some sources placing the date as December 21, 2012.)
Why did Walter Sparrow's wife choose that book for him?
It was coincidence or destiny. You decide.
What song plays when Fingerling first meets Fabrizia by the burning car?
"Tear You Apart" by She Wants Revenge.
What are the differences between the R-Rated theatrical version and the Unrated version of the movie?
The unrated version features extended sex scenes and a prolonged storyline. Altogether the unrated version runs more than three minutes longer than the theatrical version. A detailed comparison between both versions with pictures can be found here.