Character mistake: Mrs. Reynolds, the housekeeper at Pemberley, refers to Mr. Darcy's late mother as Mrs. Darcy while showing Elizabeth and her aunt and uncle the house. This is a grave mistake on the part of the filmmakers as she should have been referred to as Lady Anne, the way her sister is known as Lady Catherine. Their father was an Earl, making them Ladies by birth, not by marriage. Hence, they must be called Lady followed by their first name.
Continuity mistake: In the scene at Pemberley when Darcy gets ready to dive into the pond, notice that in one shot, he is looking at the pond, the next shot shows him stepping down, and the third shot (right before he dives) shows him looking at the pond again - in the exact same place as the first shot, as if he never took the step down.