In the scene where they're discussing who Henry the 3rd is named after Rebecca's mom mentions that Jewish people don't name their children after living relatives. This is only true in the Ashkenazi Jewish culture. The Sephardic Jewish people, however, don't follow that tradition.
"Mistletoe", the title song by Colbie Caillat, is heard throughout the movie. This was released on 7-01-2007 by Universal Republic, courtesy of UMG Records. It was written by Caillat, Mikal Blue and Stacy Blue.
During the blackout scene they say "so you chose outside lights instead of inside lights" but when the young couple go outside there are clearly lights on inside when clearly it is also stated that only the Christmas lights, fridge and freezer are run on the generator.