Trivia: Stan Lee didn't make his customary cameo as he was in Toronto at the Fan Expo and couldn't attend the filming in Montreal. He joked that the producers thought it would boost box office figures to omit his cameo, because viewers would think they must have missed it and go watch the film again to check.
Trivia: An alternate version of the film, titled "The Rogue Cut," was released several months after the film debuted on DVD and Blu-Ray. This version of the film reinstates several key deleted scenes that were removed for pacing reasons. It is also notable for featuring the character Rogue in a larger role than seen in the theatrical version.
Trivia: Getting the character Quicksilver into the film was a bit of a legal minefield. Both Marvel Studios and Fox wanted to use the character in their own projects, but there wasn't any sort of formal agreement over him. Eventually, a resolution was reached - Quicksilver could appear in "Days of Future Past," but with no references to "The Avengers" or the Marvel Cinematic Universe. And he could similarly appear in "Avengers: Age of Ultron," so long as there were no references to mutants or the X-Men.